We hide the retractor in the qtr panel. We have plates made that we just weld in . The 69-70 qtr trim is a little tough, this is why I said we will probably go with a retractable 4 point using our roll bar.
It's best to do a mock up with the old seat and everything else installed, then you can make adjustments with the seat. The seats we designed are lower and sit back and additional inch, it might not seem like a lot , but it does help.