You will definitely have more configuration options and better beam control if you go with individual 3V LEDS, or 6V etc., rather than a COB.
If you do not want to drill and tap the heatsink for MCPCB mounting, you could glue the MCPCBs to it with thermal epoxy. Use minimal adhesive, just a small spot in the center of each MCPCB. Weight them down while curing. The adhesive would not be irreversibly permanent because it will be possible to pry the MCPCBs off later if needed. Convoy MCPCBs tend to have a rolled edge, otherwise, file the edges to 45 degrees to make them easier to remove.
The heatsink could be a forged one from Wakefield. You might be able to fit one of the 130mm x 30mm ones in there, and add a fan, and cut some vents in your host. If the 130mm one won’t fit, there are 78mm and 68mm ones and so on. The fan could be powered by an inexpensive dc-dc regulator board from AliExpress.
The reflectors could be, for example S21A OP or S21A SMO from Convoy.
You could set it up with two separate drivers, with two different LEDS and optic combinations, for separate SPOT / FLOOD. The center LEDs could be floody high CRI, and the outside LEDs could be Osram WF1, in S2 reflectors or whatever.
The battery configuration could be 1s or 2s, etc. rather than needing a high voltage lipo pack. With a low voltage setup, you have a lot of flashlight drivers to choose from. Using protected cells would give you LVP, which you might want if your dc-dc regulators etc. could otherwise drain the batteries too far if accidentally left on.
You could enter this build in the Old-Lumens challenge. 