It looks like we are on the same adventure! Have you made any progress? I’m 100% new to CNC, but I have some experience with 3D printing. Plenty of overlap but I’m stumbling a lot as I try to understand many things.
I’m guessing the 2 options you are looking at are the EOT-3 and the OTK-3? The OTK-3 looks like it’s using a D-sub connector, so I’m not sure how it would interface. Similar situation with the EOT-3 and some circular 7-pin connectors 
It looks like they both have a 43mm mounting neck, though it looks like they both clamp very close to the bottom of the attachment. The custom clamp that would be required to mount it on the Foreman would need to hang lower on the carriage than the standard clamp, since the standard clamp relies on the spindle to protrude far below the clamp. I see a thread about it here. Luckily this application, at least for me (I plan to cut cardboard/chipboard), shouldn’t put a huge load on the clamp, so I’ll be modeling and 3D printing one that should hold up well.
It looks like between the 4th (B) and 5th (A) axis, only the 5th is free, so the knife orientation would have to be controlled by this. (For reference, the 4th axis output is paired with the Y axis, so each motor gets an output.)
In my searching on here, I see @TMToronto comments as the best source of info, though it doesn’t look like their endeavors were simple, and that was without oscillation.