Hello and welcome helwie44, I'm not currently working on the Alphatronic machines. It's very nice to see someone who did lots of work on those machines here though.
Eventually I'll continue to work on it (if someone else isn't picking up the driver), then I'll be sure to contact you.
The range 0x3ff0 to 0x3ffe is already forwarded to the crt registers, see
https://git.redump.net/mame/tree/src/mame/drivers/alphatpx.cpp#n65 (0x37f0 with mirror 0x800 so it's at 0x37f0 and 0x3ff0).
