I have a CT from a '69 C10 I bought last spring. It is, actually a TH475 and is a unicorn that was only used for about 18 months in '68/early '69 and the only application I can find was in a truck. They continued for a number of years in motor homes.
It has a unique slip yoke size,output shaft and tailhousing, larger than TH350/Muncie but smaller than a TH400 and the yokes have been discontinued for many years. I did find a place online that can have one machined by special order, but it costs $600, just for the yoke...
I attempted to get online info on a tailhousing, output shaft swap to TH400 parts, but didn't get any solid answers. There are a few race transmission builders who like the case, as it is stronger, and make it a 2 speed, so there must be interchangeable parts for the case.
I was going to contact our local trans builder about this, but decided, since the yoke is $600, and mine is worn, I'd rather have him build a 200-4r core I have here for the truck.