Any one know how to decode a rear end vin?

I purchased an 8.8 that i was told was from an 89gt. I am swapping out my 7.5 before i blow it out at the strip. I have a eaton locker, 5 lug 31 spline axles, and 3.73 waiting to be installed. Any help would be greatly appreciated.
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'86 Birds had a 7.5 rear,even the Turbo Coupes.OPnly the '87/'88 Birds had the 8.8,and they had either 3.55's or 3.73 gears,Traction Lock and quad shocks......oh,and disc brakes.
87/88 Tbird rear

If you have a 87/88 Tbird rear it will be 1 1/2" wider than a Mustang 8.8 rear. You will need to watch wheel /tire clearance with the decreased 3/4" per side fenderwell clearance. The emergency brake cables are different for the disc brakes. I think you will need to have the rear disc and calipers and run those instead of the rear drum brakes. With the rear disc you need to change out the master cylinder to optimize braking. (the rear disc require more brake fluid than the rear drum brakes.) There may be some attention needed for the brake fittings. (SAE vs Metric)
THe rear disc will help overall braking and decrease 60-0 times and distances. Your call; but I would want the rear discs and calipers before I put in under my Mustang.
You can install the Mustang drum brakes and axle shafts into the T-Bird diff if you want.The diferentials are the same width.It's the axles themselves that make the piece as a whole wider.I removed and sold the disc hardware and kept the drums on mine.