I highlighted the areas that I was refering to. Uless I reading it wrong, some areas area contradictory. Not picking Jimbo, just clarification. The first sentence does say 6.5/10 the you say 6/10, then the last highlighted is real confusing....9.72-6" offset?
I have true 10" wheels with 6.5 b.s. with no issues and stock spring location
10 inch will fit but it must have a 6.5" BS when using the stock spring location or 6" BS and using a true 10" wheel,.. not a 10.5" wheel when using coil overs. Not sure how that equates to mm in offset. You will need to remove the quads to run anything wider than a 275 tire back there also. I've seen 315's fit but not on all wheels. Some will rub the fender and on 87 - 93 GT's the ground effects like to rub on large wheel and tires also.
Also,.. not sure how your rear suspension is set up. But if you run coil overs in the rear in the stock shock location,.. 10.5 inch wheels wont work. 9.5" - 10" with a 9.72 - 6" offset and no more than a 285 tire or else they rub the springs