there are slightly different part numbers and bores for different years, but the largest one is (1-1/16th") ironically the cheapest also at like 50 bucks for a rebuilt one(this is why i say to ask for a 1991). I have used several of these rebuilt ones and they seem to be done nicely, with no complaints from customers. Its cheap and works great, nuff said. Im not sure about the booster though. Ive never had the pleasure of one going bad yet.