Given that Mach doesn't really care about the units, you can set the steps/unit to 1, and then your commands will simply be in steps. So, G0 X50 will move 50 steps, or 90 degrees. You can also set steps/unit to 0.5555556, and then give it commands in degrees. So, G0 X90 will move 90 * 0.5555556 steps, which is 50 steps or 90 degrees. Or, just use the A axis, which I think is already in degrees.

Regards,

Ray L.