RE: Fun Factor ST/MT Shaft replacements
I didn't use the center pin. I have had no problems with out it and Poor Judgment says he hasn't either.
As far as the grinding part just take it slow with lots of trial fits. It is easier to remove metal than to add it.
Try to remove the same amount of material on each side for the flats and I beveled the outside of the cups a little bit for clearance. You will also need to clearance the shock towers a little bit. On the ARO towers I just rounded them over a little bit.
Here are some pics that might help.
I forgot to add that I shortened the cup section to around 14mm.