i always suggest buying an aftermarket unit. they have a warranty, are brand new and have instructions to install and sometimes brackets and wiring to install them.
yes this costs more but i think it gives you more in the long run.
i love going to the junkyard for parts but when it comes to cooling i wont take chances with a fan that may have bad wiring, a bad motor, crack fan blades...its just not worth risking IMO.
that being said IF you absolutely on going this route i hear fiero fans work well but i think that's a smidge small. ive heard LT1 fans from fbodies work well.
i once considered getting a fan from a junkyard but after thinking about it and the risks involved with such used parts i went and bought an aftermarket fan. its been trouble free, came with all the wires relays and brackets needed to put it in.
im not trying to discourage you from keeping things cheap but i am saying you get what you pay for sometimes.
i think a 4th gen f-body fan would work just fine. may cost a bit though! they seem quite popular. but most likely would fit with few issues if you use a radiator of similar size, in other words not a V6 narrow radiator.
what exactly is your use for this car? if its a street car you should be able to upgrade to a stock heavy duty cooling radiator as they're made out of aluminum cores and plastic tanks. i use one for what was originally a
b-body since it had the trans fittings where g-body cars have them but it fit right in like it was for a V8 engine. i use a cutlass radiator hold down. i shaved some weight getting of the fan shroud, the heavy copper/bronze radiator and belt driven fan. freed up some power AND improved gas mileage.
i would insist on using that type of radiator. they're better than the old ones that's for sure. as for my fan i went with a black magic fan. the old 150 model. had i known they would come out with the black magic extreme i might have waited to get that one since it covers more of the core surface area meaning more air pulled through the core for better cooling but for my V6 this thing cools it down in a new york minute.
it cost me about 400 bucks to upgrade my cooling system but i also needed a stainless steel upper radiator hose as the buick V6 upper is not long enough for a wider radiator and that cost me a chunk of change i didnt want to spend. but this included the coolant and distilled water, all parts including the radiator hold down from the junkyard, the radiator, the fan, that blasted hose which cost me like 50 plus dollars. for that 400 bucks ive had a flawless 100% reliable cooling system that took weight off the car, freed up some power, gave me better gas mileage (noticeably!) so i think it was worth every penny. i'll get a pic or two sometime and show you what it all looks like. i need to redo the hold down, i did a crap job painting it on it as i was kind of in a hurry at the time to get it all done so the car because it was driven daily.