Unless you are ready to spend about 10 grand on a professionally done coating I wouldn't paint it.
If it were mine I'd spray it with a good cement sealer so oil doesn't stain it as quickly and fine dust sweeps up better and leave it at that.
Servomotorkit.com sells a rotary POT switch that probably will plug right in.
I have that setup on my 7X lathe with a switch from him. He has info about what controllers his switch will and will not work on.
I was considering doing the same with my drill press too.
I've been sneaking around here as a non-member for years.
I don't make model engines myself, but I sure do enjoy seeing the ones some of you do make though.
I usually end up here looking for some home machinist or home toolmaker type of information, which there is plenty of also.
I decided to...
While not the cheapest option but probably not priced terrible by the time you chase everything down, www.servomotorkit.com has complete motor kits or just parts to do the conversion with the ubiquitous sewing machine motors that are available online.
I bought my motor and controller off eBay...