Thank you very much for the link, TacKer... but for a programmer like me, it is almost useless. Well, I guess I will have to disassemble/reverse-engineer the GEOS file.
On the one hand, this is a royal pain in the ash, but on the other hand, it is a good exercise in 6502 ML. The main problem/concern is I can only look at the code and "guess" how it works (because I don't own a CP-F83 to verify).
I guess I should not complain: "nothing cheaper than something free."