well from what I'm finding, the early shafts were set up for a single row bearing and a chain oiler. Next came a double row bearing with a chain oiler. Next came a shaft for a double row bearing and NO chain oiler. This later shaft seems to be the latest Ks (7 and

and the first Fs (1 and 2) Need to double check the fishies. I have all three. All three will fit in my cases. I am only interested in the double row variety and now that i know there is one without an oiler I will use that.
The one I bot off eBay was identified as a K3, but the fishies show K3s had a chainoiler and the one I bot does not have a chain oiler. This means its later.
Finally I think there is a difference in the number of teeth on the drive gear at some point and you'll need to keep that the same.
Assuming the later shafts are swappable, you'd need to swap the gear possibly.
I'm still learning.