Although I do not have a comm diff yet, I had been doing a bit of research on shortening them and this is what I found.
I have not done this myself and am open to being corrected.
From what I can find out the axle tubes are pushed into the diff housing and can't remember if they are riveted or welded in 3 spots. Undo these rivets or welds on the long tube and pull it out and cut it down to length of the other side (short tube)
Push the tube back in to the housing and weld it back in ensuring that the tubes are in line. Buy another short axle slip it in and the job is done, one shortened diff.
I did look at it a whole ago but can't remember how wide it was when shortened but someone here will know. Did read that it ends up 1/2 shorter than a UC torana diff. Width of UC
??
Obviously a basic and condensed version bit you get the basics.
When you say it quickly it doesn't seem that hard does it?