On a Vintage Kart forum, one of the guys recommended vapor blasting by RestoCycle out of Tucson, AZ. From their website, I requested an estimate, supplied two photos and received an estimate back within a day. I sent four Rupp Kart Turbines in to them, and received them back with free shipping the same week. Total cost was $140. I have no affiliation with these folks, but they are easy to deal with, FAST, and inexpensive. There was minimum alterations to the surface, no removal of material, no hassles.
https://www.restocycle.com/homepage
https://www.restocycle.com/homepage