Its not hard to tell a Buick 350 or 455 from the rest of GM's brands... Look for the engine with the Dist on the front of the block. The challange is in telling the different Big blocks appart along Buick's lines. The 400/430/455's all are Identical in appearance, the only way to tell them apart without a teardown is to look above on the block where the trans bolts too... there it will have the CUI cast into housing. Ofcourse, Stamping numbers will tell also, but at the yard... this is the easiest way.
Bottom end can handle upwards of 600hp before you need to worry about a Girdle or anything... stock cranks can handle that, Billet cranks are only option if you want to go higher.
Go here for Parts:
Http://www.TAperformance.com
There are a couple others, but I can't rember the websites right now.
Go here for more info on performance option/tricks, and oiling upgrades:
http://www.V8buick.com
Just make sure you set up the rest of the car to handle all the torque..... Stock 510ft. lbs is alot for a unibody and stock trans and rear for a camaro (well, not the 1st gens...lol)