Xargon321 wrote:

it will cost you just as much to rebuild that as rebuilding a 8.8 you can find a decent used one cheaper. 8.8 came with trac loc so that's one less thing to have to buy. you can get them cheap look for people parting cars out if you pull it you're self/

X2...why not just bone-yard a V8 (8.8)rear axle and bolt it in.  I had no idea that Ford was using anything but the 8.8 in any late model Mustang. 

BB
 

The 7.5's were used a lot longer than I would have thought based on a google search.  I wouldn't put anything in that rear other than seals and bearings to keep it on the road until you find a used 8.8 that already has a traction lok rear and maybe even the ratio you want.  By the time you buy a ring and pinion and a TL carrier you could pay for shipping for an 8.8 complete assembly and have a much stronger and better rear.  Check some of the Factory Five forums for wrecking yards that specialize in boneyard Mustang parts but Craigslist with an expanded search range will find what you want or need.

You can get parts at most places for the 7.5.  If you convince yourself that you want to modify your 7.5, look here for parts and then go to Summit or others for purchase - but they also have standard rebuild parts/kits too.  I'm not sure you would like the way your V6 would perform with a 3.73.  https://www.yukongear.com/partcats.aspx?SearchMode=Make&MakeName=Ford&ModelID=275&ModelName=Mustang&Side=Rear&DriveType=RWD&DiffID=159&DiffName=Ford+7.5%22

I did some more searches.  American Muscle has a 7.5" trac lok unit for $208.  Add gears and a rebuild kit with bearing and seals and you would be ready to go.  Are you going to tackle the work yourself?  I put gears in my 1985 5.0 that had the 7.5.  It wasn't too difficult but I had some assistance with the pattern.  I was able to use the same pinion shim and had to play with the carrier shims to get it right.

I read a number of posts on 3.73 swaps and there didn't seem to be a big downside other than higher revs on the highway and a decrease in mileage.

Here is the link for the trak-lok - However, I just noticed that this is for 31 spline axles.  For your application I would simply call them and see if they can put together a package for you  http://www.americanmuscle.com/ford-31spline-88-carbondisc.html?utm_content=Driveline+-+LSD%7CFord+Racing&utm_campaign=79-04%20Years&utm_source=Google-pla&utm_medium=Shopping&utm_term=%7Bkeyword%7D&AMID=ford-31spline-88-carbondisc-GSBasicFitmentV1&year=2000&T5_Var3=blue&GID=24062

Not exactly right but close - a source for gears and track lok

http://philadelphia.craigslist.org/pts/5337825124.html

and another    

http://philadelphia.craigslist.org/pts/5349270436.html

And a GT being parted-out

http://philadelphia.craigslist.org/ptd/5365688965.html   
   
 

All Mustangs from 1979-1985 came with 7.5" rear ends. In '86 and beyond, all V-8 Mustangs received 8.8" rear ends.

Fox 5.0L GTs all came with a Traction-Lok differential as standard equipment. Traction-Lok was optional (not standard) on 5.0L LX Fox models.

V-6 Mustangs through 2010 received the 7.5" rear end. Beginning in 2011, all V-6 and V-8 Mustangs were being equipped with 8.8" rear ends.

'79-'04 Mustangs with a solid axle housing had 28-spline axles --except for '03/'04 Mach 1s. They had the heavy-duty 8.8" with 31-spline axles.

2005-present V-8 Mustangs have 31-spline axles.

2011-present V-6 Mustangs have 31-spline axles, with the 8.8" rear end being standard equipment in them.

Traction-Lok in V-6 models was optional up to 2010 and standard since 2011.

Ford being Ford, there's also the issue of housing/axle width changes between Fox, SN95, S197 and S550 platforms so, this is something else you'll have to pay attention to if swapping an entire rear end assembly.