There is no "spindle" on a FWD car like these. The carrier (which is short for "wheel bearing housing with carrier") is the large cast part the wheel bearing presses into. But the hub inside is the same, and the standard issue 1.8t and VR6 front outer CV joint is the same, hence it being an easy upgrade... you needn't even take the axle out of the car, just pull the whole assembly loose from the control arm and strut and swap it over.
The inner CV joints can be different, depending on model/year, but in order to make use of any of the larger ones you'd also need the flanges from the transmission, and I really doubt that is much of an upgrade anyway, as a lot of the later AWP cars use the stupid plunge style tripod inners which seem to not hold up as well nor are as easily serviced as the Rzeppa style joints.
The transmission itself, the 5sp, is geared far too low to be of any use with a TDI... and even the later 6sp units the GTIs, NB Turbo S, GLIs, etc. got would still not be geared appropriately nor worth the hassle.
OP, keep in mind that the 1.8t engine was an option on GLS Golfs and Jettas, but the GTI/GLI with the same engine may have some different goodies like slightly sportier springs, sway bars, etc. Just depends on the car.
I have front brakes from a 2000 GTI VR6 on my Golf, springs all around from a 1.8t GTI (AWP engine). But a GLS Golf, even with a 1.8t engine, would have used the same springs as my TDI GLS Golf used.
