One way is an item called a 'coupler' I think. There are three pieces to it, all plastic.
One fits over each shaft, and the third joins the other two via two or three knobby protrusions. If something locks up either shaft while running it simply shears off those protrusions and you replace that piece instead of serious damage to either machine.
You might check out some of the larger equipment places [MSC or Enco] under power transmission, or drop a note to Rob Frink and see where he suggests checking. Rob is an extremely valuable resource for many of us.
If I were setting it up [as I did on my old Grizzly]I would use a step pulley for variable speed, use one of the twist belts and mount the motor either right above or right below the grinder to keep it off the work surface.
It took me a long time to realize I needed different speeds, now I would never use a grinder that did not have that capability.
I hooked my new KMG up to a variable speed DC motor and I like it real well.
Good luck- post a pic when you get it all set up and working
Dave