RPM

Pretty sure Midlife answered it. It's the highlighted print in the original quote. 

For sure without Mike it would never have happened.  He is a sheet metal genius....
 
 

I guess with 6 years I am a newbie, a lot more to learn.

Try running with the gas cap open/off. This will eliminate fuel tank venting as the cause.

The simplist and without mods would be that C4, if he rebuilt it correctly. While it may not be the optimal transmission, I'll all for getting these Mustangs on the road without necessarily building the perfect car. 
 

I have built 2 cars so far, a 1969 mach 1 and another I won't describe here, I fought a low vacuum condition on both because of high performance engine. I am with Bob, if I built another  one I would do manual disk on front drums on back. If you build a performance SBF with vacuum assist brakes you may wind up doing a lot of this 
 

The simplist and without mods would be that C4, if he rebuilt it correctly. While it may not be the optimal transmission, I'll all for getting these Mustangs on the road without necessarily building the perfect car. 
 

I drive my 69 daily and would recommend stock factory parts. Preferably from 1969. I put many Mustang parts on my 69 from newer Mustangs, but it's a lot of work and sometimes affects a few other parts and modifications. If you want front discs I'd use some from a 69. I have manual discs, which make it easy to stop. My brother has manual drums on his 69 SCJ which work as well as mine. Adding power brakes sounds simple enough, but is a lot of work and involves different parts, pedal, pedal hanger, booster etc.

I drive my 69 daily and would recommend stock factory parts. Preferably from 1969. I put many Mustang parts on my 69 from newer Mustangs, but it's a lot of work and sometimes affects a few other parts and modifications. If you want front discs I'd use some from a 69. I have manual discs, which make it easy to stop. My brother has manual drums on his 69 SCJ which work as well as mine. Adding power brakes sounds simple enough, but is a lot of work and involves different parts, pedal, pedal hanger, booster etc.

C4 is the logical choice. Find out what year it is, as there are several types of C-4 transmissions out there, and some of them are actually C-5s.
For sure should bolt up to your 302.
If you have the original flex plate, keep it and use it.  Later automatic transmissions could have a different "balance weight" than the older cars.
I actually have a c-6 bolted up to my '69 351 W block, it fits and works fine.  A C-6 is likely overkill for your car, and actually the C-4s can take plenty of power.
 
Vic

Don't forget the FMX, that's what came behind the 351W in my Mach. They are strong and reliable and should have the same bolt pattern as a 302, since AODs fit all these blocks, the FMX should too. I'd stick a 4R70W on there, as its the last and most perfected version of the AOD- then you get overdrive.

While we're on the subject of solenoids, I would recommend to anyone who has an older Ford vehicle with the solenoid mounted on the inner fender to occasionally have someone start the vehicle while you observe the solenoid. This should be done with the ambient lighting low enough to visually observe an electrical arc if one is present, preferably at night.
I had an older Mustang with the original solenoid still in it, no problems with starting at all. My Dad started the vehicle while I just so happened to be looking into the engine bay and sure enough, a large arc of electrical current ran from the housing to one of the mounting screws. After close examination I could see a small fracture had formed in the housing after about 50 years of age and heat cycling.

I would go with tan cloth top and tan vinyl/cloth seats. All vinyl or leather seats will be too hot to sit on when parked for a few minutes with top down in summer.

Looking for some advice from this knowledgeable community.
First, thank you to all the regular contributors to this site. The information you post has help me immensely on my car over the last few year.
My build is finished from a body and mechanical perspective and I'm now working through design and planning on the interior.
First here is a picture of the car.
 The intent is to have a more modern approach to the build. With the roof I'm leaning towards a more modern finish and going with a canvas material rather then the traditional vinyl. Has anyone here have advice on which manufacturers to go with and is this a good idea?
If this was your car what color would you go?
Black
Off white
Tan
For interior finish, I'm currently leaning towards a custom made tan interior. I was recently told that vinyl material would be better for a convertible and leather will get damaged in the sun quickly. Anyone have any experience thoughts on this? 
Would appreciate all feedback as I'm struggling with next steps. 
 
Cheers
Don from down under.

Don't know if it will work in your case or not but I have gained a little more clearance by removing the transmission mount bolts. With my foot put some pressure on tail of transmission and actually slide it over some. I was taking my header out bottom tho. If you just need a tiny bit more clearance at back part of engine it might allow you to remove from the top.   

Also got my passenger side dash panel attached, final item was to install the screws to attach the panel to the map light assembly.  Used 1-1/2" #6 SS Pan Head Sheet Metal Screws with #6 SS washers, so it would not damage the paint.   Came out good.  Installed my "Mustang" emblem on the dash.   
 

More good info:
https://www.deadnutson.com/1969-70-factoids-1/

Wow! The best until today I'd heard of was my neighbor who got 12 years out of his OE on his Toyota pickup.
 

I had a Nascar select by interstate in my 78 ford pickup got 9 years out of it and i was very happy with that ,most batteries today if you get 4 years you are lucky 

Back in 2006 Checker Auto Parts was marketing "84 Month Autolite" brand car batteries.
Logo on the side of the case had a classic look to it, so I bought one for my '69 Mustang and one for my '67 Fairlane in early December 2006.
Sold the Fairlane in 2010, so I don't know how long that battery lasted but the one in my '69 was still cranking strong this summer.   Not a ton of miles in the past 17 years but it has always been plugged into the same classic 1.75A Battery Tender year-round.   Cleaned up terminals once a year and topped off with distilled water when needed.
Well, it was last driven sometime in September~October with no issues and this past weekend it was time to put it to bed for the winter and "no-crank".   Cleaned up the terminals, and still no-go.   Put it on my bigger charger and got it up to 80%, dropped it back in and it cranked but very slowly.   
This battery finally gave up the ghost ... I don't think I've ever had a car battery last this long !! 
I now work at a CarQuest auto parts store so a DieHard Gold replaced it.   Never was a huge DieHard fan when it was part of Sears, but it is now just a name owned by Advanced Auto Parts (as is CarQuest) and the batteries are still made in the same factory as the former CarQuest brand batteries were.
Doug    
 
 
 

Used #6 SS Pan Head Sheet Metal screws 1-1/2" long, with #6 SS washers.  From local ACE Hardware.

More good info:
https://www.deadnutson.com/1969-70-factoids-1/

Love that look. I did the door inserts in the same silver as my gauge bezels. 

Cool tip. I did not know that book existed. 

Installing my kick panel and vent mounted speakers