The issue is with the 5sp t/case.
The gearlever boss is pinned to the the selector rail which runs through the t/case and into the 5sp box.
The larger 3.15 low gear will foul on the gearlever boss so the bottom third needs to be cut away and new mounting holes drilled and tapped into the selector rail.
We were initially thinking of selling the modified selector rail and boss as part of the kit. Of course the auto & 5sp t/cases all need the grinding of the housing selector rail boss as shown in the above pics. When we did the 3.15's for my 95 5sp Mark did this mod for me.
Initially he wanted to only make 2.7's for the Gen 2 & 3 because of this issue but I talked him into the 3.15's so I'm surprised that he's decided to switch to the 2.7 ratio (this being the next lowest gear size module).
There has been a few guys that have done the 5sp conversion.
From memory the Trooper Tera low range kit includes a modified selector rail/boss for the 5sp.
I'll give him a call to discuss.