The lazy way to do it would weld some covers over the front axle outputs on the tranny, put some CV axle ends in the front hubs, and weld the center diff. Then you're RWD. But you're gonna break stuff. You could get a super-built tcase that'll hold the power but who knows how the rest of the system will. A built tcase is gonna run you a few grand at the least though on top of the expense to put in an AWD system. You don't have to use a gvr4 drivetrain though, I think a 1g gsx drivetrain is mostly identical but you might have to use the vr4 prop shaft. Hopefully a more knowledgeable forum member could help you out some more with the specifics