I am also running jag ifs and used 1.25" adapters on the front to convert to ford 5x4.5 and I used 2" spacers on the rear to clear my bag mounts and tuck the 2005 mustang "bullet" wheels in the rear fenders without having to instal huge tubs in the rear.

 

I used 1 1/4" spacers also, a lot depends on your wheels too. The backset can make a big difference. I have a TCI front and with the same backset wheels I had to use the spacers on the back to keep the same track front and back. And the driveshaft offset makes no difference.