Welcome to the site.
Look for rust. That's the main thing. alot of times the windshield seal will leak, or the door seals, or the gaskets were the wipers come through. sometimes all of the above.
Head gasket/ warped head a can be another problem area.
Pretty much any luv you find will most likely have a cracked dash and dried up door seals.
oh and carburetors sometimes aren't the best...
Best advice, look it over really well. If it runs drive it.
as for a v6, if i was going to put one in, it would be a carburated 4.3l chevy. with a th350 or 700r4 trans.
As for parts, some things can be difficult to find. Ebay is your friend, along with the classifieds and wrecking yard here. Also salvage yards wherever you live. There are things that can be had at parts stores too, alot of times you'll have to wait for them to order something though...
Good luck! (it's really not as bad as it may have sounded

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