The UK cars (300GTs) come with 282bhp rather than the 276bhp of the imports (GTOs). The turbos are slightly bigger but to little benefit due to the additional catalytic converters. They all came with 4WD, four wheel steering, ECS (adaptive dampers) and the leather interior as you mention.
They never came with the combat rear wing - the mk2 body styling was carried through to the end of production in 1999, hence the 1993 onwards cars with integrated headlights have the actiove rear bootlid spolier, not the hoop spoiler (mk3) or combat spoiler (mk4).
My 1994 mk2 has mirrors with electrically adjustable heated glass that manually fold. The early mk1s had a switchable exhaust, but none of the mk2’s did (nor late mk1’s I don’t think). Most are running something stainless steel by now anyway.
The brakes were common across 3000GTs and GTOs -some time around late 1992 the fronts were upgraded from 296mm 4 pots to 314mm versions (caliper is the same). At the same time the rears were changed from single piston sliding claipers to two piston fixed calipers. I believe the disk size stayed the same.
Likewise the change in the design of the engine’s bottom end from 2 bolt to 4 bolt happened around the same time on GTOs (1992 ish). Based on e55t33’s comments, it may be all mk1 3000GTs have 4 bolt engines because of this, certainly my K reg one did. There is a thread on here somewhere on how to distinguish between the two visually.