there was no 3.70, the standard was 3.90 with an optional 4.11 .... if you want the engine to last a long time, it'd be "comfortable" at 2500 and a max of 3000, and don't expect to be cruising at more than 55, especially with stock brakes
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics
