I can tell you that you can indeed install a 428CJ with C6 bolted together as long as you are very careful, and take your time. I installed mine with both exhaust manifolds on, and with the steering box in place. I did however loosen the master cylinder (power brake car), and I am pretty sure I took the drivers side valve cover off, but it may have been the passengers side due to the heater motor. You need to get the back end of the car jacked up as high as possible, keep the front on the ground, have a good jack ready for the transmission, and ideally have at least 3 people on the job that know how to install motors in cars. It took the three of us 2 hours and 20 minutes to do it, and didn't scratch anything. We used cardboard to help with scratches, which I would highly advise. I can send pictures of this if you like, and you will definitely need to get the motor/transmission to at least a 45-degree angle or it won't fit.