I then worked with Porchy to add both the new tunes to the arcade rom by means of a replacement of the 64Kb Z80 rom with a new 128Kb one on a carrier board. This was necessary as the 2 new tunes wouldn't fit into the original 64Kb rom alongside the existing 3 tunes. Porchy did the necessary alterations to the Z80 address decoder GAL and designed and had manufactured the rom carrier board and I did the alterations to the Z80 and 68000 code. To select the new tunes simply put the gear shifter into the HI position and steer left and right on the music selection screen. The whole lot was completed by the 26th March and it's been running in my cab ever since. At the same time the fixed PCM audio ROM was extracted from the 3DS binary.
Of course none of this would have been possible without the power of MAME and its debugger to assist along the way. So thanks a million to every single MAMEdev out there who's ever contributed to the project, no matter how small their contribution.