/6 to V8

I'm planning on doing an engine swap down the road and have a couple General Discussion type questions. Are the parts (V8, transmission, 8 3/4 rear end) pretty easy to find, either here or on ebay? What is the best engine and transmission for the price, availability,and compatibility? Thanks for your time! I'll have lots more questions when the time comes (after I pay off the body shop (vinyl to hard-top conversion, pics to come))...Hope the mole rat doesn't offend anybody!