MATT W. - Todd & Steve pretty well answered Your question about the KT-17 series I & II engines. Series I engines are what early jd 317's came with. Local shop back in the day said a well cared for KT-17 series I was ready for rebuild around 1000-1200 hrs. jd 316's & 318's had ONAN engines which IMHO are a worse engine. IH only used them in the 982 and a few in the later 2072's for a short period of time.
Like I said yesterday common attachments like mowers , snow blades, snow blowers, moldboard plows, tillers, are easy to find, demand has driven up the $$$ the last couple years.
There's a lot of common parts between the green & yellow/white tractors, engines, hydro's, wheels & tires. Gear drive CC's are however in a class all their own. I guess that's why quarter-scale pullers are after them all the time. I personally think IH has a better attachment mounting system, no tools required, more commonality between tractor models, You can switch between attachments in only a couple minutes. Kinda like IH's Fast Hitch they built on full size farm tractors back in the mid-1950's till the 1970's, Pretty much "Click & Go!"
JONATHAN W. - No locking differential in CC's, unless You want to make it a "LINCOLN LOCKER". With proper tires & weighting they really aren't necessary IMHO.