I have done a few mods on less than stellar 2xAA lights. The problems you will run into… You will need to find a suitable buck driver for a 3V led, so a 2S 3V driver. The switch will have to go, or likely you will melt it down. I have had good luck spacing in an Omten 1288 with trimmed nylon washers, the retaining ring you have may be good enough work, but it will not be metal and will not be able to conduct to the contact ring on the switch. The MCPCB looks pretty straight forward as does the driver retaining ring. You may have to open up the driver retaining ring to allow for back side components based on your driver selection. I assume that you do not have a good selection of mod parts yet, some left over parts may solve the switch retaining ring problem in brass, but would have to be the right thread.
Some sources for the random parts for your mod kit would be…
Fasttech
Their presence here
Banggood USA site, more on Chinese site
Mountain Electronics, good state side supplier
I do not know that light, but I would caution you that this may not be a good first mod candidate.
Good luck, Matt