I have a PU-20 NTSC-J frankenstein console with non-NTSC-J bios soldered in place of original, for the purpose of installing this modchip. Unfortunately, PSone PAL was the only chip I could salvage right now. I used Pro Mini clone (Atmega328P) Physical installation went smoothly and PAL games booted...

I just did a swap on my 7000 PU-20 to BIOS from broken 102 PM-41 I had lying around, it seems to work just fine, if anyone seeks a confirmation. Obviously it doesn't boot anything without modchip, as PAL games are blocked at Mechacon stage and NTSC-J are blocked by BIOS, but at least with this BIOS ...