Jeff "Gatecrasher" VanOrsdal
We'll begin with the exploded diagram of the entire 3S uni-body. (180k image) You'll notice at the far right of this image, there is a whole subsection devoted the the AWD specific parts. Some parts like #24 and #30 could probably be modified to accommodate the AWD system. This is only the beginning of our problems however.
In this second diagram, we begin to see the complications as the rear of the car is isolated. (83k image) The most noticeable difference is the shape of the frame rail, #11. Also of not is the fact that #21 on the AWD chassis is not present on the 2WD chassis. This part is replaced with #13 on the 2WD chassis
In the third diagram (92k image) compare the differences in parts 1 and 2 on the 2WD chassis with parts 1,2, and 3 on the AWD chassis. Also compare the differences between the frame rails on the 2WD chassis (#3 and #4) with the rails on the AWD chassis (#4 and #5)
In the final diagram (89k image), we see the most obvious difference so far. compare the shapes of parts #2 and #6. The #6 reinforcement is completely different, and the #2 strut tower mount is at a completely different angle.
The last consideration is the cost of parts. You'd need an AWD transaxle, transfer case, driveshaft and the whole rear suspension cradle (photo coming soon) and countless other small parts like bolts and mounting plates. If you're using 1st gen donor parts, you'd also have to find a way to lock down the all-wheel steering system since the NA engine computer does not have the programming for the system, not to mention the difficulties in plumbing the thing.
Unlike the turbo system, this is far from a bolt-on procedure. You'd spend far more between welding, parts, and labor than you would on a whole new VR4, and you would still be lacking the other options the VR4 (Or RT/TT) would provide.