ol' 55,
The original 6.70 x 15, 4 ply passenger-style tire had a 28" outer diameter (unloaded) and a 5" rim width.
The original 6.50 x 16, 6 ply truck tire had a 29.10" outer diameter (unloaded) and a 5" rim width.
Wheel offsets were approximately the same.
Tim
