You're welcome. The OP may have forgiven the side tour.
It's tough to be new to a highly technical forum. Advice: google it and read, read, and reread.
A brief thought from the MTBR forum (see link in paragraph if interested), about using the existing heat sink. You likely will have enough clearance to reuse it. However, it doesn't contact the body behind the mounting flange apparently. Bad for thermal management. Maybe a split-ring shim that can be closed enough to pass by the flange but snap out to the walls and give a tight fit to the original heat sink would work, with some Arctic Alumina thermal paste to fill gaps. I did that with a copper pipe for my light. Then you'd only need a flat disc of copper or aluminum to take up whatever amount of space you need to mount
quazzle's unit.