I put a 400 in my 67 GMC with a 400 Turbo
Started as a low budget 60k mi. engine and a quick fun project
Used the frame mounts from a 73 -87 chevy truck with the clamshells and the engine mounts from a 75 Catalina.
I used exhaust manifolds that exit in the rear
This is how it sits now, I had to pull it back out and rebuild the engine because it smoked ,flat cam etc.
Just got it tagged and insured, waiting for the seat to come back from the upholstery shop
Good Luck