The Mk3 probably had a Jetta syncro version in the US, but I don't think I've seen one over here.
Converting a front wheel drive car to 4wheel drive will mean that you have to cut the chassis to fit the drive shaft to the rear.
You'd probably have to do something special to mate an RS4 engine to the running gear in a Rallye, finding a gear box to take the engine's power and fit in the engine bay along with that big engine my be difficult.
Would the running gear from an Audi S3 Quattro fit a Mk3 Golf/Jetta ?