A wee little update with both good news and bad.
The good news is that something akin to a Malkoff boot fits perfectly in the HDS except it lacks the nub to actually let it press the button, the button is 14mm wide and the rim/flange/whateveryouwannacallthething is 19mm in diameter and 2mm thick, make of this information what you will.
Indexing the PCB after putting it back was made through this process, you'll have to follow this very specific process and it's so advanced you might want to read through this twice. Ready? Ok, you tighten the PCB and retaining ring until snug, put it on the body, check high and low, if both are fine you're good to go. If either isn't as it should be, adjust it by then instead, first snug it down.
I've yet to receive the o-rings, but looking at the spare parts for the Malkoff and comparing sizes i'm half sure already that 20,57x1,78 will work in it, otherwise i'll just have to get others and keep trying. It's a fun experiment regardless.