Just so other people don't make the same mistake I did. There are two different sized pinion flanges, the actual Cobra diff uses a 4.25" bolt pattern and the lincoln/t-bird diff uses the smaller 3.5" bolt pattern.  I didn't specify when asking Samberg for a driveshaft flange to go along with my 8.8 mount kit and he assumed I had a cobra diff.  Not a big deal and the parts aren't expensive but if you are swapping to an 8.8 just be aware and make sure you measure your diff flange and specify which one you have. 

Yea the cobra and some trucks use the larger one.  3 inches by 3 inches.  The smaller diff flange is on the reg mustangs and smaller 8.8s  2.5 by 2.5  bolt hole to bolt hole.   I made the same mistake, the grannys torque arm wouldnt go around the larger one.

It is always a good idea to measure the companion flange on 8.8 rear ends to verify what pinion flange is needed. The critical dimensions are the bold circle and the center register, which aligns the flange. The U-joint size is also important to keep in mind. As I recall, the stock Cobra pinion flange use a 1330 u-joint, but I bet you can get a 1350 flange as well.

Andrew