All 2 bolt Ford starters such as the ones on a Fox, F150, Lincoln, etc only come in two different pinion offsets. The starter housing can varry in size but will have only two offests. You may be running the wrong offset. If your running the 3/4 offset and need the 3/8 offset, the pinion gear will miss the flywheel.
1990 Mustang Gt: Stock block, Scat 347 RA, All forged internals, main griddle, AFR 185 heads, 1.7 rr, all an fuel lines, 30# FRM injectors, Holley 255lph fuel pump, Performer Rpm II, 75mm BBK TB, BBK CAI, 80mm promaf, Pro Billit dizzy, MSD blaster coil, MSD 6BTM, PA c4 with trans
brake and 3500 stall Mac shorties, Mac o/r H-pipe, Mac mufflers and tail pipes, 3.73 gears, 3g altenator, aluminuim radiator, Zex 125 wet kit tuned by XXX motorsports with SCT chip. 306.08 hp/ 311.26 torque