As I recall the little 610 and 613 Fullers were used with Gasoline or small V-8 Diesels such as the 3208 Cat. These engines all turned 3500 rpm at least.
When you put one behind a slower turning 6 banger it makes the shifts empty quite mean, and it will almost bind even while trying to skip gears.
It is driveable, just not as smooth as the bigger 10-speeds would be.
Also any that I drove had the little air button for the clutch brake so you had a half a chance of getting it into gear... . I don't know if that was someone's better idea or if it means you can't put a normal clutch brake in there. I would want to know that right up front before I installed one or you would have to shut the motor off to get them into gear. They were awful without a working clutch brake.
Mike.