The bolt patterns are different. The t-case shifter for the BA10/231AMC bolted on the inside of the 88 XJ but there's no where for it to bolt on the inside of the 91YJ. The T-case shifter for the AX15/231J bolts on top of the AX15/231J. Thats why it won't work. Plus the location of the t-case shifters are different. The t-case shifter of the AX15/231J is directly to the left of the gear shifter. The 91YJ was made for that on the inside and the 88XJ was not. The t-case shifter for the BA10/231AMC is diagnally down and to the left of the gear shifter. The inside of the 88XJ was made for that and the 91YJ was not. If i put that on the inside of the 91YJ i believe i would have to cut out room for it then i would have to figure a way to bolt it on the inside.

The t-case shifter plaste for the AX15/231J bolted on top of the AX15/231J. The t-case shifter had two bolts and the gear shifter plate has 4 bolts. But the left two bolts of the gear shifter plate is the same two bolts for the t-case shifter. The bolt pattern is square.

The bolt pattern for the gear shifter plate of the BA10/231AMC is diamond shape.So i can't bolt the t-case shifter plate to the BA10/231AMC b/c of that.

Plus i cant swap linkages for the t-case shifter without rigging it up some how.

In other words the t-case shifter and linkage is vehicle specific as well as transmission/transfer case specific.

I believe a need a t-case shifter and linkage specifically for the 91YJ with a BA10/231AMC. I don't know if they make that b/c its unusual for a 91YJ to have a BA10/231AMC.
I will also need a t-case shifter and linkage specifically for the 88XJ with a AX15/231J. They should make that b/c that isn't unusual.