Buying a 360 engine, need advice

Like Oldmanrick said make sure it isn't very rusty. Rust pitting can cause major issues. Also make sure it doesn't have an excessive ring ridge as the newer blocks don't like to be bored more than .040 max. Mileage will generally dictate how much cylinder wear there is. I usually pass on blocks with more than 150,000 miles but that's JMO. Look it over for any cracks, especially on the deck surface and in the lifter valley. Also remember that since it's a magnum block you won't be able to run older LA heads because magnum's oil the rocker arms through the pushrods while older LA's oil through the block, which the magnum doesn't have the provision for. I didn't see you mention heads but just so you know magnum heads were very prone to cracking. Aftermarket is the way to go for magnum heads. With RHS and Engine Quest making them now at decent prices it's no big deal.