I've put a page up with detailed pinouts for the PC Engine series of chips, including the Hu6260, Hu6270 and Hu6280. This is for all PCEnging, TurboGrafx, Vistar, and other systems - the chips are the same throughout.Have a look
There are also more notes to be added - I have several pages of notes I made when doing these pinouts, and a few quite detailed schematics.
If anyone wants to double check my work (hah!) please do, it's bound to be full of errors. The SuperGrafx schems, specifically, are almost certainly completely wrong, and probably dangerous to even look at.
(The schems are coming soon)