Frugality required

A T-86 can be used with a small indexing hole 18 transfer case. You simply substitute the T-90 rear bearing retainer for the T-86 unit that indexes the large indexing hole 18 transfer case. Not the best choice but can be done if that's what you have. You can also make the large indexing hole 18 fit a T-90 by installing the T-86 rear bearing retainer. Been there done that in both situations and it works fine.
You cannot do this with the T-14 or T-15 as the indexing rings are completely different.

 

I have a '68 CJ5 225 V6, T98, 32" tires and Saginaw steering with everything including brakes in excellent condition, and in the shorter early CJ5, anything over 55 to 60 is asking or trouble!!

 

I feel that the short wheel base CJs handle well up to 65 MPH even with a Ross box if all is in good shape.

Yes Nicks right.
If you modify the T86 AA with certain T90 parts it will mate to a small hole transfer case.
You can also mate a T18 to a small hole case if you slightly modify by using the T98A rear adapter plate.
My previous reply concerns the various stock transmission configurations.