Reply to Pioneer EFX-1000 Mod -- Question about Sanwa OBSF-30 Button Clearance

Hi, I'm modding a Pioneer EFX-1000 to use an arcade button as a Tempo Tap button. I'm explaining the whole situation because, with DIY, very-detailed community posts have always been a great resource for me.

(History: The Tap Button is the weak link of the unit. On half the used ones I've run across the Tap button stops "springing" mostly because the recoil mechanism is a 10 cent micro switch mounted to the main PCB, and actuated by a fragile 3mm plastic peg. To add more fun to the mix, the Tap assembly is held in alignment by two tiny, unrepairable, plastic pins about 1mm in diameter each. If either pin breaks then the whole thing becomes wonky.)

I'm removing the entire (broken) Tap assembly and wiring a Sanwa OBSF-30 in place. The first problem is that there's 28mm of depth in between the top of the EFX-1000 chassis and the PCB. As we can see from its datasheet, the OBSF-30 needs at least 32mm of clearance underneath:

http://www.in2amusements.com.au/datasheets/obsf-30.pdf

So, I'm using Front Panel Express to fabricate a Perspex "riser ring" that will both give the button the depth it needs (I'm going with a total of 37mm to be safe) and make the hole diameter correct (29.5mm in this case).

I'm using the "snap in" type of Sanwa button. According to the documentation , this button can snap into a surface anywhere between 2mm and 5mm thick. But, the total depth of my "riser ring" is 9mm. So, my idea was to make the first 3mm of the ring (the entry point the button drops down into) 29.5mm in diameter, then expand the diameter to 33.5mm, then at the end of the "tunnel", drop the diameter back down to 29.5mm.

My question is this: does the part of the button shaft just below the "locking clips" require a certain hole diameter? I can imagine a situation where insufficient diameter would "pinch" the clips shut and prevent the button's locking action from working.

If a larger hole diameter is required for the space below the "locking clips", does anybody have any idea how many millimeters of depth this diameter is required for? Unfortunately the drawing does not provide enough detail to determine that. If someone has a link to a "true datasheet" for the Sanwa buttons I'd appreciate it.

Thanks for your time -- and I'll definitely post pics once the mod is done.
rs