Has anyone tried adding a dimmer switch to adjust the RPMs?
Yes and no. A cheaper, Router Speed control unit will not work and will burn up your motor pretty quickly. I tried and returned this one:
https://www.harborfreight.com/router-speed-control-43060.html
They make much more expensive motor speed controls, but those were more than a new motor (at least the last time I researched).
I just ordered two, 6" arbor extenders from Jestco. The arbor's from Caswell were only $7 each and $14 for the Jestco extended units. But I thought the Caswell arbors would be too short. The shafts on that new motor were 5/8" and 1/2" and Jestco had one for each side.
I have my high speed bench grinder on a free-standing pedestal mount from Harbor-Freight. Its' too short for pipe work (too low). I may have our welding shop add an extension to it, so it is just above waist high and then leave the other buffer mounted on my table.