I know from experience that the montana subframe bolts directly up to the grand prix. Main difference is that it has the mounts for the 3.4. Probably would be best to lay the two subframes side by side and see where they've modified it to clear the driveshaft.
As far as the transmission, yes, it will directly bolt up. The main issue is that at least on the aztek's the body control module plays a part in controlling the awd. Not to mention, that there is not tuning support from hptuners for this. You could try messaging them, but I doubt they would go through the trouble unless you're willing to pay through the nose.
I'm sure if you beat on the underside of the car enough you could get it to fit after a LOT of fabricating, but the rear would be really tricky to fit in there. I'd probably look more into the aztek/rendezvous with the independent suspension/air ride if you're going through the trouble.
The biggest issue is that these things were never designed to take any power whatsoever. They frag on the stock 3.4. They're really just not built well. Personally I wouldn't waste my time on it, but it would definitely make a good project albeit futile!
