Well the lathe is gone now, along with the t-slot (traded for that shear) but here's what I can tell you.

I had to drill or mill out a portion of the underside 'cuze the thing the compound turns on for angles isn't easily removable. Then in the top of the cross slide I drilled and tapped 4 holes for 1/4-20 cap screws to hold in sorta the 4 corners. I used the two existing holes on one end of the t-slot but since it was a bit too long I had to cut it off and I drilled and countered two more holes (same spacing as the existing ones) and drilled and tapped the cross slide there too. It was very solid and when I prepared the lathe to sell it, it was easy to pop off the t-slot and put the compound back on. And since the under side of the t-slot had the space milled out, there was no question how to put it back on.