Your confusing the tecate 3 with the machine I have wihich is the atv kxf tecate 4. The tecate 3 was able to interchange tranny gears with some of the kx250's. The tecate 4 tranny is completely different from the tecate 3/kx250's.
Flyin Hawaiian sounds like you may have verified what I needed to know. Your telling me if I were to buy a 1980 kdx250 tranny it has 6 gears correct? That will be my starting point. I was pointed in the direction of early to mid kdx's without being told specific years. I believe based on what your saying early to mid would essentially be 1980-84 for the simple fact that they share the 6 speed gears.
Remember lads. Not to be confused with the kxt250 tecate 3. There are virtually no similarities between the T3 and T4. The kits that flyin Hawaiian speaks of were deff for the T3 not the T4, that I can personally verify.
The KDX250 had a 6 speed up to 84, That was the last year for it in the states until the 91-94 watercooled KDX250 came out. I had a 84 KDX250. Totally differant bottom end than the Tecate but who knows it may work. The Tecate trans was actually offered in kit form as a wide ratio kit for the 85-? KX250s for those that wanted to convert them for offroad use. I had a wr 4th and 5th in my 86 KX250. The ignition/lighting coil/flywheel from the Tecate was also offered as a kit for the KX250.