I have two of these in my cab which I ordered from Chris at Ozstick and they're great. They look ultra close to what was in my cab originally and are set to take 20c coins by default - what would you want to change that for?
I'm unsure about whether or not you can adjust them, all the screws appear to be glued in place from what I see. And from what I can gather, remember this is a universal fitting coin mech - when operators wanted to change coins in real arcades they simply changed the mech. By that I mean the back part the coin drops through. I've seen various ones selling on ebay that take 10c coins etc. Out of the two in my cab one took $1 coins and the other 20c pieces.
My advice is to ask Chris directly because he's somewhat of a guru and a speedy responder to boot. I could be wrong about what I've said above. Either way, let me know what happens here and if needed I'll drag out my old beaten up mechs and study them too.
Aussies unite!