when i was looking, ebay is usually good place to start, ive actually found one on craigslist also. But im sure others have better ideas to look
Junkyards, peoples yards (usually find the best deals this way as many people want the car out of the yard........pronto), or the local want ad paper
i agree with everything said above. without mods to the engine bay a 302 would be perfect for you. 351 will work with some hacking at your shock towers. one thing to keep in mind : stock 302 block is rated at 400hp and can stroke to 347, 351w is rated at 700 or 750hp and can be bored to 427 or maybe more. just kind or depends on what you are looking for. My girlfriends grandpa has a stripped out street Mav with a beefed 289 that can get the front wheels up, but on the other hand theres no replacement for displacement!
Talk about digging up the dead . If you have a question, just start a new thread. But yes, a Boss 302 will fit. But cutting the shock towers just plain makes life easier for any V8 when it comes to working on them.
If I were to do another motor swap, (budget permitting of course), I would be inclined to go with another RC107 suspension conversion and the ZZ460 - which is based off of the Boss 351. It advertises 575hp/575trq. That would be sufficient to move the <3k lb chassis and the buttocks sitting on it rather nicely.