Yup for an adapter. Way back then, I remember doing a lot of measuring etc before I was able to determine which adapter ratio was best for me, but now it is spot on. Now, using a GPS speedo to compare with your truck's speedometer will help determine what direction you need to go, and much easier. The link that Otto supplied above will have more details. Also for those deciding to install larger or smaller diameter tires, will also run into this issue and must plan to go the adapter direction.

Craig

My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear
My truck ....... Respect The Rust
If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.