-First ask yourself what you are going to do with this car. The following is assuming you have no overdrive, if you do than you can step one level higher in rear end gears. If you are going to all out drag race, you can go as high as 4.10 or more if you want; this will be okay on the road if you don't go on the highway for extended periods. If you are going to drive this thing on the highway and still want to race some, then get something in the 3.55 to 3.89 area. If you want total economy on the high way than something between 2.73 and 3.27 is good.
-The next thing to consider is what kind of differential you want. If you have a good deal of power and want to race then you will need a positrac or limited slip(same thing different name) If you want all race then get a locker but this will be distroyed by turning if you drive on the street. An open rear end if the cheapest but most of the power goes to only one wheel. If you really want to shell out some cash, an airlocker is cool. You can lockup the rear for racing and disengage it for street driving.
-After all this, decide what kind of power range you expect on having or do have and how much abuse you are going to give this thing. Big power and abuse from racing or will need something strong like and Ford 9" or something custom. If you have moderate power than an 8.8" Ford will work nicely and can be built up to take some power. If you drive like Granma Jane than a 7.5" Ford from an early model Mustang will be cheap but may be hard to find parts for.
-Nascar runs modified Ford 9"s and most guys who are non-brand biased (chevy, mopar, ford) will say that the Ford 9" is one of the best units to have. Of course there are those guys that are all GM biased that say that the Ford 9" are crap and there are guys that say that Chevy 10 bolts are crap but talk to a professional that specializes in rear ends and He'll probably say the 9" is the way to go. Good Luck!
[ May 26, 2002: Message edited by: blown69stang ]</p>