Okay...so that is MT on the outside, and round with a flat side to match the mill on the inside??  Then where does the drawbar go, down from the top of the spindle? 

oops....looks like John already answered that.   

So, does that mean that the collet is tightened by the bolt pulling it up into the MT, squeezing it tight on the mill?  

I think maybe I'm seeing how it can work....now if there's just a hole in the top, all I need to do is find some appropriate collets and I might be in business.