For someone that has this working, could you please post the key elements of your config.txt.
I am trying this with a g07 monitor but can't get a full size picture, nor will it sync properly.
Pi 3 with hdmi_group=1, hdmi_mode=8 for 240p
Hdmi to vga adapter, the typical cheap model on ebay/amazon.
ultimarc j-pac with the 15khz jumper in place
jamma video wires running into the g07.
Other pcbs work with the jamma harness including original pacman pcb, so I know the jamma harness and monitor are wired and working properly.
I am in the US so SCART isn't really an option.
thank you.