Something else to consider...
The buick/olds/pontiac/cadillac bellhousing pattern is different from the chevy pattern. Those engines will not match up to a chevy transmission. I've seen a 455 olds in a 2wd pickup, but the transmission was also the olds bolt pattern type. Before chevy started using the 6.2 diesel they used an olds 5.7 diesel, in 1979-1980 or so. I think the guy used those factory 5.7 olds motor mounts on the 455. The olds deisel equiped trucks also had the b/o/p/c transmissions, I guess they were turbo 400s. I dont know if they made any with the 4x4 tailshaft.