rear ends
 

OK I wanna know how you tell if an axle is 7.5 or 8.8?

The differential cover on a 7.5 has two flat sides (top and bottom) and two curved sides, the 8.8's cover has all sides shaped the same.

Also there is a tag attached to one of the bolts of the cover that has the axle size and gear ratio. Reads something like:
7 LS 5 3 08, which means 7.5" limited slip, 3.08 gears
8 LS 8 2 73, 8.8" limited slip, 2.73 gears.

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GT-40 heads (ported, polished, + milled), B303 cam, 1.7rr's, JE pistons, Offy intake, Carter AFB 625cfm carb, Flowtech 1 5/8" shortys, Flowtech X-pipe, MAC Flowpath exhaust, MAC pulleys, 373's, subframes, Eibachs+Tokicos, B&M ripper, FMS Clutch, Zoom Quadrant+cable, 17" CSA Ultra rims, 235/45ZR17 Yokohama AVS S4's, MSD 6A ignition+coil, FMS 9mm wires, Carbed, Naturally Aspirated, and Nasty!

1980 that should be a 7.5 in there if it is stock rear end.

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14.28@103.0 on a G-Tech Engine: Steal Mounts, Under drive pulleys, K&N, Home ported Lower Intake, No power steering, No A/C
Drive Train: 3.55, T-5z,

Real power STUFF I Have and will put some time: Mac cold intake, 70MM TB, Valve covers (COOL ONES)255 Fuel pump NOS Dry 75HP, AFR 165 58cc, GT-40 Intake.
Next to get: Rocker Arms,Cam,Injectors 24, What might I need???See It at www.computerconquest.com

Thanks for the info guys that really helps