It's likely that is is mostly just the standard Microsoft Basic with some modified I/O routines. Since Microsoft Basic is now under the MIT license you are free to modify the code, it may be relatively easy to re-implement the I/O routines and have a legal 'recreation' of the P2305 cartridge.

This particular machine is Z80 based and not 6502, so it's not trivial to port.

I've looked into building my own BASIC implementation and got quite far with that. Unfortunately, most games that were written back then rely on timing that is near impossible to recreate at that level. Emulating cycle exact Z80 behavior and then having the original BASIC routines on top of that is a far easier route.