Hi there,
Personally, I have installed the RamJET into a 1981 with the stock TH350 transmission.
Its a wonderful swap.
Issues are as follows.
First, the hood will not clear it, unless you shim it UP.
And even then, we had to slightly chamfer the TOP of the manifold, where the throttle body bolts to it.
A higher rise is in order for the hood.
The air cleaner will JUST clear the radiator fan, about 1/4 inch.
The TH350 will handle the power, as long as your not going drag racing.
It would be suggested to rebuild it, as thats how I did this swap.
The engine is smooth and tractable to 5500 and we get about 20 highway with the stock gears at 60 mph.
Allthebest, c4c5