Ed,
I had a '62 GT Hawk that I put a 401 Buick in with 2x4's. Fit like a glove except for the passenger side exhaust manifold. It hit the frame rail, but that was with the original Buick manifolds. Still to this day one of the best sounding engines I have ever heard. Someone made engine mounts that allowed it to bolt right in with the original mounts, I can't remember who right now but I will rack my brain for awhile and see if I can come up with a name.