normally they are all the same size, but you will probably get problems as third party controllers use different contacts than original ones.
most ps2 controllers use membrane contacts.
I'm switching out the whole interior save for face buttons. I've already looked inside the PS2-controller I have now, and yeah, it's an electrical membrane contact sheet.
Also not all genuine PS2 controllers have the same internal design. My original black one (from an early fat PS2) and my silver one (from my slimline PS2) have slightly different sizes of parts and different mount places for them. Swapping guts from one to the other would require a bit of work with a dremel I think.
Yeah, you're right, but drilling a new whole or two, or filing down some PCB wouldn't be a problem, as long as it would fit in the original PS2-controller's case

Could you not just buy a used PS2 controller? They're pretty cheap where I live, like a few ? for the standard black type. Unfortunately for me the silver ones are more expensive but still cheaper than a knock off.
The prices of the controllers themselves aren't the problem, the shipping costs are, and I'd rather buy a new knock-off than a 10 year old used genuine

Also, I've already ordered this thing, so.. I'll have to work with it :p