There should be a plate on the side of the transmission that will ID it. The Roadranger RT910 trans is a 10 speed, made for many years, and it uses an air shift range selector mounted on the shift leaver. The RT910 is as common on a diesel as a SM420 trans. is on a Chevy, parts are plentiful and good used RT910's are cheap. Its bullet proof, just make sure you keep it filled to the proper level with mineral oil. You'll rarely use 1st gear since its so low.
I just reread what you had to say about your trans, a T handle on a cable shift sounds like an earlier R96 roadranger 10 speed trans. They are the earlier 10 speed type, the transmission is long and heavy, strong and bullet proof just like the RT910. Both are direct 1 to 1 in 10th gear. We used the R96 on early White 9000's 'coupe cab' type, 1962 models we bought used in 1972. Great trucks, great transmissions! I still own one 1965 White coupe cab, will post pics of it one day.
Beautiful truck you have, would love to see it one day...
James
