Well from what I've read, putting any other final drive behind a EZ30 besides a 3.70 will make it scream on the freeway. I miss having the RX dual range box in my coupe as it was great behind the EA82 SPFI engine that was in it.
I'm also curious as to different gear sets from EJ transmissions and how they bolt into the XT6 case. Also, I'm curious about swapping 5th gear with something a bit taller, again to help with freeway rpms.
Oh and I forgot you had that adapter plate:headbang:
Any Phase 1 gearset will drop into the XT6 front case halves (phase 2 got a beefier reverse gear, and therefore the idle shaft is a bit further away from the main shaft. no way to get around this in a phase 1 case). Center diff and housing will have to match front pinion shaft, of course.
I ran my '88 XT6 with trans internals from a '94 AWD Impreza. 4.111, I think taller 5th than XT6. I loved it, don't remember what rpms I was turning on the freeway, but no complaints.
If you're planning a swap, I'd baby this trans until then. Fresh fluid (Extra S!), and be a little gentle on it. It'd be worth it to be able to use an EJ pressure plate with a new-gen H6!