I have a 99 olds 88LS trans. Trashed. Trans shop (friend of a friend) delivered a used one to replace original. Everything has gone smoothly bolting back in with the exception of the passenger side trans to subframe mounting bracket that bolts to the transmission case. The bracket has 3 bolt holes, all that are flush, bolt to a flat surface, none recessed. On the trans case only the two bottom bolt holes match up and one of them is recessed, deeper then the other, and the 3rd or top bolt hole aligns with nothing, there I'd no bolt hole threaded or otherwise in this position. Question being is there a possible other bracket that could have been used to mate up with a slightly different the housing that gm used? I know this trans was used in several gm models.
Everything else, trans to motor, trans to subframe, wiring connects etc. match and fit correctly.
Any info greatly appreciated, hesitate to go any further in the case I have to unbolt and remove redo more then I've already done.

Welcome to GM Forum, Dave! We hope you'll hang around after your transmission is installed.

As far as that goes, is your new transmission from another '99 88 LS; identical year, make, and model? GM is known to make tiny changes from year to year. Worst case, it'll work just fine, but you'll have to fabricate or replace a mount, or invent some kind of adapter to make it fit perfectly.

I'm wondering if the output housing is different, but I have never heard or seen of such thing. And I'm on my 3rd transmission myself.