You can buy the interface ready made from monster joysticks and it's a lot smaller so maybe easier to fit... £9 for the interface £4.50 for the 1.8m cable. £19 if you get the interface, wiring loom & cable so about £26.50 per joystick... cheapest new replacement I've found is £39 but that is a SNES style KTRL CD32 - Dunno if you deleted it or it was a YT glitch... if it was you I'm sorry for putting it back... I'm not spamming just pointing out alternatives as I was looking into this for myself as I have 3 CD32s. (Removed link to monster joysticks as I think YT spambot is killing the comments - Products>Accessories & Spare Parts>Interfaces & Wiring Looms>CD32 Retro Joystick Interface)
It looks like cool project, but in all honesty I would rather add extra $20-$30 to buy case which would better accommodate proper buttons and extra PCB board.
I coincedentally ordered a few black joystick wires from aliexpress a few days ago. and after You spoke about the pinning, i counted that all 9 pins are wired. so I tried to put the link in here but the page was no longer active anymore. bedauerlicherweise. but what about those sega genesis pads on aliEx.? would those work on Amiga or will these destroy the 8520 'ers , I remember there was something of with Sega vs Amiga.
I think the 5V is wired in a different way and it could fry the Amiga. RU-vid does not allow for links in comments anymore except from the video creator. Of course it does not tell you that when you write the comment. It just does not post it.
@RetroWK OK, I'll stick with my Competition Pro Pad then! I guess once you monetise the RU-vid episode you've made enough money? Impressive all the same! [Edit] PM me if you change your mind! Would be ideal for Final Fight Enhanced and even better for Fightin' Fury CD32!