This is one area where the type 89 has a serious advantage over the type 85 (quattro, anyway).
The 4000 quattro shifter linkage is more complex than the oil drilling subsidy regulations of the US government. It is difficult to access to refresh and lubricate for better shifting, and also tough to picture how to easily shorten the throw of the control lever. The 90 quattro is as simple if not simpler than the two wheel drive (type 85) coupe. The lever you hold goes through a plastic bearing, and is bolted to an arm that bolts to the transmission control shaft. That's all there is to it.
Replacing the connecting rod is not very difficult, so long as the hardware holding your catalytic converter to your downpipe is not totally rusted solid. Mine was just replaced with stainless since it was apart for a clutch job, so that was easy. Undo those bolts and free up the OXS wiring, drop the front of the exhaust, remove the heat shield (six 8mm nuts) and you are in there. It is easy to undo the two bolts holding the rod in place. The new rod may be about $100, but its u-joint bushings will not have any excess play in them. The transmission end only attaches one way, so aligning the shift lever is simply a matter of getting the rear end of the rod bolted on the same way, and is pretty forgiving while you align it. I threw in a new boot while I was in there, although the old one looks fine still.
The shifter throw can be altered by shortening the top of the lever arm and lengthening the bottom. While the rod is disconnected is the time to do this!
Basically this involves removing the lever, by unscrewing the shift knob, removing the shift boot (find the hidden screws...), pulling the snap ring that is on the pivot ball and lifting it out (assuming you have already disconnected it from the rod underneath). You may need to remove the pivot ball housing as well.
With the lever out, you do two things to it. First cut a bunch of extra threads on the top with a die - they are 14 mm I think - you can go for about 3-4 cm - and cut off about 2.5 cm of the lever with the die in place. Removing the die will clean up the threads where you cut the lever. This step will lower the knob and lessen the actual distance it travels while shifting. Then go to the bottom end of the lever and find the pair of holes through which the bolt holds it to the rod under the car. You can drill a new set of holes about a cm or slightly more below these, taking care to get them neat and straight. Using these holes will lengthen the lower portion of the lever, decreasing the angle through which the lever must be operated in order to achieve the same linear motion of the connecting rod.
Combining these two steps will result in a lowered shift knob (by whatever amount you shortened the lever) and less angular throw between gears.
You will probably also have to take the white plastic filler piece that fits into the top of the shift boot and cut off the extended tube that goes down around the lever itself - since you have removed this extra chunk of the lever. When reassembling, be sure to get the lever relatively centered, and make sure that the reverse lockout functions properly. The two bolts that hold the ball housing in place have these weird spring washer things that lock it laterally - I have found so far that pushing the lever to the right as if headed to reverse (with the lower rod firmly attached) positions the lever correctly. Don't be afraid to check to make sure you like the knob position, and loosen everything and readjust it if you don't.
It took me about 3 hours to do all of this - 2 hours for the under car work of swapping the shift rod and about an hour of messing around with the lever.