Hi,
It's quite easy once you get it (not that easy the fisrt time, but after a few trials, it's ok). Remove the rear diff (2 screws, 4 if you're using anti roll bars), remove central shaft drive cup (only 1 pin to remove) and center shaft, unscrew the spur gear holder, you can get the rear axle out and you got your spur gear holder free (unscrew the top deck if you're using a big spur).
have a look at my article
here . I know it's in french, but the pictures are easy to understand and you still have babelfish to translate...
RCBuddha : I've found the SD very responsive to the positioning of the suspension arms (you can either move them forward or backward, 4 mm overall) and this alllows to change the mass balance. This summer, I had issues with my rear tires overheating and screeching after 2 laps, giving a car very fast for thse laps and mainly undriveable after.
Moving the rear arms 1 mm backwards (thus having less weight on the tires) allowed me to keep the tires at a lower temp. After that, my car was perfectly consistent during the whole heat (without heat ahahah), no screeching from the tires at all and amazingly fast.