Well, I spent a fair amount of time on Lock'n'Chase Aquarius with graphics and so on, and it looked just *awful*.
So I'm going to shift the platform to the Jupiter Ace and try that instead.
I think the Aquarius is one of those platforms that rather than try to produce something that looks like the real game, you work within the limitations of the graphics hardware to produce something that plays similarly.
So anyway, the code has been converted and hacked up yesterday and now works very nicely, though there's some optimisations to do. One of the things you can do with the Ace is because it is FORTH, and most 8 bit CPUs can't do FORTH well, it has routines to do things like push DE on its internal stack.
This is called by RST 10h (or 18h, I forget). Rather than simply execute the code, I can replace this with C which is functionally equivalent and get a speed boost for fast mode on the ESP32.