I have seen several at shows with BB in them. Seems like they are usually running a smaller booster and of course the exhaust is always coming out in front of the rear tires. http://www.rustynutscarclub.com/jm59el.htm You can see in these pictures it is tight.
A 454 will drop right in using existing v-8 mounts
A booster nor larger than 7" will work----might as well not even have one.
(mine is about useless)
If you have a 2-speed wiper motor, HEI will have to be clocked so the electrical
connections point to the front of the engine.
Exhaust will be an issue-----most stock manifolds will not work
Only a few people make headers for this application.
Very little room between #1 exhaust and the upper control arm
I used Sanderson cast iron block huggers and am happy with them
Small starter is a must if you ever need to service it.
Mechanical clutch linkage will not work with these headers.
If you have or are considering rear disc brakes (again--not happy with mine) you will get no larger than a 2" tail pipe past the rear tire.
I have 2-1/4 exhaust thru the mufflers ans step down to 2" after the mufflers.