you can put a 302 gmc straight six in there for more power or if you look around the bellhousing from a 55-59 chevy with a v8 should let you install a 454 using stock parts.
you would need to fabricate some 55 chevy style front mounts to bolt alongsode th etiming chaincover (front of th eengine)
You might even find a 292 straight six to put in there.
Even so switching to an automatic and v8 isn;t too tough but swapping that body to a modern frame is a bitch and the end result is always some kind of frankenstein cobbled up
Im not saying you couldn;t do th ework good, Im saying the new frame under the old truck looks...not right.
something like a crown vic, plymouth fury torsion bar, or mustang II suspension fitted into the old frame looks 100 times more sano than a subframe job or a frame swap.
My brother just bought a guy out of a 56 chevy truck project it has the original I beam front axle but with disc brakes and power steering. it has a kick ass old chrome decorated tilt telescopign column from an old caddy