G1 A *********x (where *********x is a multiple of 360 and a number close to the existing A axis DRO reading) #99803=0 %
This should rotate the A axis to a multiple of the zero position with minimum rotation then reset the A axis DRO to zero. You could then goto zero on the other axes in the usual way.
This demo was made in the early days, before the M62/M63 commands were included within Mach4. The laser was switched using the A axis direction pin and machine control was by the LPT parallel port using Darwin.
All Mach3 Gcode must finish with a CR so it is usual to insert a null character such as % at the end of every file. If you do not do this then the last line of code will be ignored. The Diagnostic LED's do not always work as expected so a Meter (or similar) connected to the mapped Output Pin may provide a better indication. You need to be using Mach3 version .056 or later.
I am not sure my family would fully understand but this guy deserves every credit for his determination to build the CNC machine of his dreams. I certainly wish him every success and hope all goes well with the build and also that he manages to find some space to put it when it is finished.