Tough questions..
I'm not sure about the brakes,some might be interchangeable,like putting 14 bolt backing plates on an older Eaton style axle..(3/4 ton 8 lug)..not sure about 1/2 ton stuff..you might be better off just swapping in later axles complete...
As for a 455 Buick,Olds,or Pontiac,they all have the same bellhousing,but its a different bolt pattern than Chevy's use..you'll need the adapter to bolt them up..a stock manual tranny and flywheel from whatever make 455 you use will work,but you might have to shim the flywheel away from the crank,
to make up for the adapters thickness..
You may be able to use a stock B-O-P bellhousing ,but the SM465 chevy tranny has a larger "hole" for the front bearing retainer..same goes for a blowsheild..you can have the hole enlarged at a machine shop to fit the SM465 though..
I'm pretty sure others here have swapped in other GM big blocks besides Caddy's ..maybe one of them will post up and tell how they did it...
