I have a 70-71 buick 455 that i would love to put in my new omega. The omega had an olds 455 but the block was cracked. Will the buick fit? Are the mounts the same?
The mounts are different, but places like TA sell 455 frame mounts. The engine itself will fit but accessory brackets and wiring harness stuff will be quite different. Keep in mind, the fuel pump, distributor and starter are all on the opposite sides of the engine from the Olds. They won't have any frame or body interferences, but the wiring and plumbing will need to be overhauled.
Engine frame mounts are usually bolted in. The proper short Buick 455 mounts are cast iron or aluminum and unsuited to be welded to the steel frame. The tall 455 mounts are steel, but they place the engine up higher and you would likely run into both firewall and hood clearance issues.