1970 dually ID questions

[marknjamie]

I just bought this truck on Sunday. It has twin hydraulic two stage cylinder dump bed with a 250 6 cyl and top loader 4 speed. It's a 1970 one ton but has C10 emblems on the fenders and what looks to me like 1968 grille trim. It also has the cab roof lights with the raised sheet metal mounts stamped into it as a tonner would. Anybody know a sure fire way to i.d. the year and series of one of these trucks? I have had a half dozen 73 to 87 GMs but this is my first 67 to 72 and I' not sure what I have. I'm suspicious that someone has changed the body at one time but everything seems to fit as it should. At first glance I was suspicious that it was a 20 because of the front wheels but they stick out past the fender an inch or so. The door tag says 10000 GVW and the VIN tag matches the title. By the way, Anybody know what years of dually wheels will fit these trucks? Thanks in advance.