I bumped it up to 15V and now the test mode appears to be dumping the ROM! I have a whack of data coming out the RIOx pins, about 20.8ms long with a bit time of approximately 10.2us. This divides out to around 2040ish bits!
Do we have any ideas on dumping the pre-Microchip PICs (ie, back when they were made by GI)? There's one that was used in a lot of mid-80s Macs I'd love to have the real code for eventually. I don't mind sacrificing one to decap, but not having to do it would be even better