the is a fill plug on the diff casing. you'll need a few different tools to do a gear swap. a dial indicator with magnetic base, a set of calipers, a pinion depth gauge, some way to remove install bearings, a shim kit with new crush collar pinion nut etc, and some marking compound so that you check the gear pattern. You can go a much easier route (this isnt the proper way to do it BTW) and just reuse the factory shims and it may work just fine. There are alot of people that do it this way its up to you if you think it will work. The best way to do it is to to check the backlash pinion depth etc using the tools mentioned above. Theres a good article in the tech section on how to do an 8.8 gear swap.
A forum community dedicated to Ford Mustang owners and enthusiasts. Come join the discussion about performance, production numbers, VIN decoders, modifications, troubleshooting, power adders, DIY tutorials, and more!