The suggestion from Dennis using a bench vice, if you have one, may be a good one for you. I have done it that way and use either the Shopsmith Wrench or a 12" Crescent Wrench which with it's longer handle gets my hand further away from the blade. You still might want to keep those gloves handy to protect from accidental slips since you could be working at a bit of an odd angle with the vice. If that won't work for you than I would suggest having the arbor and blade on your Shopsmith without the blade guard to hold it while you use two wrenches (1 on the base, 1 on the nut) to loosen or tighten the arbor nut.
Mark V completely upgraded to Mark 7
Mark V 520
All SPT's & 2 Power Stations
Model 10ER S/N R64000 first one I restored on bench w/ metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ metal ends & retractable casters.