When I built a swing valve housing for my turbo, I used a valve guide out of a Cat engine. It happened to fit the swing valve shaft and we had them in stock (since I work at a Cat dealer). Can't remember what the application was, but I'm thinking it was for a 3116 engine. I do know a 3306 engine has a 3/8" I.D. guide. We have them all stocked pretty close together and I just pulled drawers out until I found one that fit. Drilled a hole in the housing (1" plate stock) and turned the O.D. of the valve guide down to a press fit in the lathe. Chopped off what I didn't need for length, and drove it in with a hammer. Dunno if that helps or not, worth a shot. -Chuck