Yes the 8.8 will fit in the car. you will need to chop off all the old mounts and weld in new spring pads. also the wheel backspacing will be affected depending on how wide the new unit is. the advantages of the 8.8 are that there is a ton of aftermarket support out there with gear sets and lockers,  you can beef it up substantially with a bearing girdle and c clip eliminators

The 8 inch that you already have is essentially indestructible up to about 350 horses as it is a downsized version of the 9 inch and has the added advantage of having a quick change center carrier that is handy when racing.  Unless you are well over the 350 horse mark or making big v8 torque you may want to stick with the 8 inch.   it is also a clipless rear end so if an axle explodes it will not drop the wheel off the corner of the car.

good luck with your modding

OhSix'

get a 9 inch from an early mustang 65-73. its narrow enough to fit and will take the pain. the 8.8 without a girdle isn't really any stronger than the 8 inch you already have. plus ratio changes require setting the unit up again. if it is a track only car spool it to boot or have 2 pumpkins. one spooled with track gearing and a 2nd locker/open for street use and fuel mileage.  only takes about 20 minutes to swap the carrier

OhSix'