Here is a link to an EBay add for an illusive vertical head drive gear for a K&T 2H mill. In the description he describes how one machines the gear to fit a standard 50 taper holder. You could do the same thing once you determine the DP & # teeth required for the missing gear (and after you make said gear - or have it made).
Find many great new & used options and get the best deals for Kearney Trecker K&T 2H Milling 30Tooth Spiral Drive Gear for Vertical Head 23653 at the best online prices at eBay! Free shipping for many products!
www.ebay.com
Here is a video of Keith Rucker with his drive gear on the K&T
So yes, not impossible to make it all work - just a lot of unknowns right now that would require quite the bit of reverse engineering.
I wonder if the Modern Mill is some sort of licence build from another manufacturer, perhaps out of the UK?
If you end up getting it, perhaps a collaborative project to help you out?