A good turbo to look for is a T04E off a heavy duty Ford truck (F600-F800 diesel). It's only capable of about 450 hp on a 302, but it's a good start. It's also upgradable if you're looking for more power down the road, and it's a T04 frame turbo, so it's interchangable with all the popular Garretts, and Turbonetics T-series turbos.
A good size turbo for a stock type 302 is a 57mm-66mm. This is the size of the compressor wheel. Obviously the larger the number, the more air the turbo can move and the more power it's capable of. The "57" is pretty small and is the one that is only capable of about 450 crank hp. I really doubt you'll find anything in a wrecking yard any larger than that, that you can use.
The best source for good used turbos is the internet. Either Ebay, or some of the mustang forums (classifieds), or even the turbo buick forums (classifieds). I have seen a lot of great deals floating around. I personally paid $700 for my T70 brand new in the box. Which may be a little out of your budget I don't know, but it's a great deal for what it is. I have seen 60-1's (over 500 hp) for around $425.
As far as a/r, that's sort of hard to say, but the most common is a .96 on the exhaust side. I have run a 1.00, and am currently running a .81. There isn't THAT much of a difference to really be concerned about it right now. The smaller the a/r, the quicker the turbo will spool up, but you may lose a little power on the top end.
__________________ Mineral Grey 2003 Cobra
THP Twin Turbo
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Mineral Grey 2005 GT
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