Matteo Marioni tested the VBI injector board with his MACH 3 game and saw that the picture number is being properly decoded most of the time with a few occasional glitches. Without disassembling the ROM, I cannot say how the game hardware uses the picture number, but I think it is fairly likely that the VBI injector solution probably would work fine for the game "as is." What stalled Matteo's tests from proceeding further was that the audio data decoding was not working. We think that the problem may be inadequate audio amplification from the Raspberry Pi.
So MACH 3 is looking pretty good but we don't have it working correctly yet.