I don't know about a comanche, but the fastest car I have ever been in had one of those. It is a 88 Firebird with a turbo 6.0 LQ4, making 700hp to the flexplate, he runs mid 9s in the quarter. Plus, besides the turbo and a cam, the motor is completely stock :eek:
Just saying there is an incredible amount of potential to these motors, but personally if I were to do it, I would run an aluminum 5.3 for weight savings, and it'd probably get way better fuel economy than the 4.0.