I got my triple XPL-HIs from Mountain Electronics, soldered and ready for parallel. I also got the Carclo optics from there. A few notes on your project…
You mention you would like throw and a good hotspot. I wouldn’t put those two terms in the same sentence as a triple. You might get less spill but the hot spot will be a lot wider, no matter what LEDs you use.
I have no experience with the F6, but you will need some sort of spacer to fill out the empty space once the reflector is gone. I think one of the main reasons why the Convoy series is popular to convert to triple is because there are spacers available. I wouldn’t have a clue if they will fit in a F6. You might have to find another solution, like soldering copper washers or using something else from the hardware store.
The F6 on FastTech looks like it has AMC7135 chips. If you can solder you could try stacking them, but as that driver looks single sided and you want a pocket rocket you’ll probably need to replace it. Most triples are run on FET drivers. If the driver in the F6 is 17mm, Mountain Electronics should be able to provide you with a driver flashed with the firmware you will need for side switch only. Maybe this one: 17mm & 20/26/27mm single-sided DD/FET driver release: A17DD-SO8 / A20DD-SO8 / etc
I haven’t seen a F6 so I can’t help you with your F6 specific questions. You might be able to find some info of use here: Roche F6 disassembly? Switch, driver, tail. and here Roche F6 hacking