I have done this swap on a 51 Chevy 1/2 ton panel truck and the motor fits great…a little tight if you use a column shifter (like me).
Through trial and error I found that a TransDapt tubular engine swap crossmember
for a Ford 460 can be easily trimmed to accept the Buick 455 using stock Buick
motor mounts. The motor mount centerline (17 1/2") for the Ford 460 is almost identical
to the same dimension on the Buick (17 3/4") ….. You'll have to elongate or ream the Ford crossmember about 1/4 to 3/8 of an inch to accept the Buick dimension.
Also, you'll have to trim an inch or so off each of the Ford engine mounting perches; so that the stock Buick motor mounts will sit squarely.
This arrangement eliminated the need to trim or remove any part of the stock frame cross members.
Lastly, get your self an oil filter re-location kit to eliminate the headache of
oil filter interference….. I put mine of the inner fender where its easy to service.
Use the stock Buick exhaust manifolds with 70-72 GS down pipes. Use a firewall mounted master cylinder to make space underneath for exhaust pipes.
To save space upfront at the radiator , I used a good sized trans cooler mounted to the rear of the trans, where the panel's fuel tank used to be...
hope this helps
