Could be wrong but I think a pad hack may be your best option if you just want to use your NG stick on a PCE. You can buy Brook converters for various retro consoles which are great but they only accept PS3/4, XB sticks AFAIK
Yep. I've seen the brook ones. Shame they are only for modern controllers. I've found a pc engine PCB in eBay. Perhaps I could butcher a Neogeo extension cable .