hi
i haven't built a cnc machine but i use them for a living (wood machinist)
one of the things i have picked up along the way is how to read g coding on the specific machines i use (fanuc controled heians)
if the coding is the same\similar as that used by cnc\dnc programs that you use then i can offer my services on how to chande\modify coding for those of you that havent picked it up yet.

The G-codes I use on the Three Axis machine are generated Automatically from a DXF to G-code or TXT to G-code etc. (several free grograms available), and Can be eisily Modified in Mach2/3, and I also use free CNC Simulators which will ley you see in 3d that the run will look like and if it does not look proper alows you to edit it and rerun it most are very simple to run, i was able to pick it up in less than a month of off and on usage in my spare time.

Joe