Here is your problem.
91-97 SER 4.17D FD
91-93 G20 4.058 FD
94-96 G20 4.176 FD
If you try and get the gears out of the 91-93 G20 gear box and put them in the SER gear box the pinion shaft will not line up with the SER FD. To put the 91-93 G20 gears in a SER gear box you will have to press the gears of the pinion shaft and put them on the SER pinion shaft.
91-97 SER 4.17D FD
91-93 G20 4.058 FD
94-96 G20 4.176 FD
If you try and get the gears out of the 91-93 G20 gear box and put them in the SER gear box the pinion shaft will not line up with the SER FD. To put the 91-93 G20 gears in a SER gear box you will have to press the gears of the pinion shaft and put them on the SER pinion shaft.