I can not tell you where to send a carburetor for overhaul but I can tell you where NOT to send one. The business name is Wyoming Carburetor Technology. I sent them a running carburetor and they damaged it beyond repair and would not make it good. They run an ad in Hemmings motor news.
Jim
I've had luck with Pinellas Carburetors. They redid my single barrel and my father has had several 4 bbls done by them. They aren't alwasys perfect, but they do a nice job. They have a few locations in the Tampa area. I forget which particular one did mine. Good luck.