I'm not convinced it was supposed to cut on the top surface, but rather, suspect that the makers used the carbide blanks they could find, or had on hand. Looks to my eye like a basic 80 degree diamond blank, or maybe an insert meant for a top-clamp type holder.I agree with that Trev. The top cutters are proud, but they also angle up toward the root. So it would cut a sloped top on a T-slot. Maybe on purpose?
I'm convinced that the top is intended to cut too. Too much trouble to make it like that if it wasn't needed. But for what?
It's definitely a weird tool!
FWIW, I would consider seeing if the centers in each end will clean up well enough to stick the thing in a lathe and turn it down to fit what tool holding you have.
Or, just park it with the rest of the 'stuff' that looks too good to chuck, but isn't currently useful enough to be really needed!