The riser under the headstock is .435", which is between 11mm and 7/16". I have a couple of QCTPs, so making a matching riser seems like a great idea. I can use the dovetail headstock as a tailstock.
There's another option, too. I have the standard headstock riser block and QCTP riser block, but not the tailstock riser. Perhaps I'll get one and if it looks like I have a use for the dovetail headstock I can make a custom riser for it.
Lots to think about.