Hmmm, there were versions of Racermame to combat the fact a lot of older games with the hi-lo shift had the same single switch closed for lo, open for hi or vice versa. I think that's been put into mainline mame now. I certainly know that playing chase hq with my sequential, i hit the same direction (up) to change gears between high and lo each time. If i'm in hi, i push up and i get lo, and if lo i push up and get hi. There's no onscreen indication either.
You might try something like joytokey, that will see the apac, and probably allow you to set keypresses and duration. Or if not, autohotkey will let you set duration with the command "setkeydelay, 0, 50" where 0ms is time index when the press is triggered, and 50ms is when it's released.
Then we need to think of a way to get the keypresses to activate in a meaningful way using something like autohotkey.
I think the problem is with game tho, and the fact you can only set the one gear change command. Because even if you use joytokey to set the same keypress to more than one position, you can still wrongfoot yourself so up is down by just leaving the shifter in the wrong position when the game boots, etc.