I did trace the pins, but haven't double-checked everything. I'll type it up and let you know. It does look pretty standard.
Seems it's same as tntell:
// R10: TMS5100 PDC pin
// R9: power-off request, on falling edge
// R0-R8: input mux
// K: multiplexed inputs
// K4: TMS5100 CTL1
// O3210: TMS5100 CTL8124
I see O4 and O5 on the output PLA too, they're not connected?
BTW David do you want credit in MAME whatsnew? I'll put in anondumper for now.