Early 64/65 A833 to later gear conversion?

Yes, it is possible, but you need the entire gear set including the cluster gear. If you want the slip yoke, now you are talking mainshaft and tail housing. If you go with the small 66 67 A body mainshaft and tail housing, they are not too expensive. Sometimes you can find a C or B body trans cheap for the donor gears. I'm not sure you will be able to see much of a difference for your time and money.