I don't know if there are any remaining audio issues with Crazy Balloon. Just mentioning this video in case it may be of some limited use for comparison purposes.
Brings back memories of playing this at a Straw Hat pizza parlor in late 1975. By summer of 1976, I recall many of the Hi Way sit down cabs at places I went to were likely converted to Night Driver cabs by then. That bummed me out because I prefer Hi Way myself.
With Hi Way / Highway, being a single board, non-cpu game (and supposedly not using any roms) and with schematics around, it has a better chance of being emulated compared to other harder-to-find non-cpu games.