Phantom, 2.2 and 1.5 all share the same effective length of 235mm.
All I really wanted was the hole spacing on the Graham mount. Someone on another forum has advised the holes are spaced 90 degrees on a 2.200" bolt circle.
This gives about 40mm between hole centres - making it a tight fit over the slot. If bolt nuts are attached it looks like they may slightly overhang the slot. Aesthetics aren't going to be great either, as old bolt holes and some of the SME cutout will be visible.
My best option (of course) is to get the Phantom with the SME mount and avoid any issues.