Hey JBT, I think with a '54 you are in luck per the crossmember at the bellhousing has mounts on a slant as do the later trucks. So a 50-60s V8 bellhousing should bolt right in. I'm sure others will be along to add more. Re. the steering box, a buddy of mine use the 55-56 exhaust manifolds that dump out at front on that side and may have fudged the box outboard as well and there may be aftermarket headers also.

It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed