A 455 Olds to 454 Chevy swap is as difficult as changing over from a Ford.....

Literally nothing works.

Some things to consider;
PTO, Exhaust, Electrical wiring harness, Distributor, Fuel pump, Motor Mounts, Alternator Mounts, Cooling system, accesory drive pulley....Hell the holes in the stringers wont even line up when you get new mounts...I think the only thing that will carry over from the Olds is the carburetor and maybe the alternator.
Its almost like a complete re rig and a lot of work, but IMHO worth it in the end... I am not trying to discourage you from doing it, but do some research first....

Really hate to see someone jump in balls deep and run out of parts/money before they finish.

Oh yeah, pics or it didn't happen..

GT