Are you using the decompresison valve when you pedal? That should negate the added compression due to the milled head and get the motor to turn over better.
And again, are you 100% freaking sure the motor itself is turning over, are your lights lighting up and can you see the flywheel spinning over and does it sound like the motor is turning over (it's pretty loud on a stock pipe even without combustion).
How does the spark plug look, it better be new, after all of that? Is the diode spark arm thing wet with gas? If not, you have a fuel flow issue. Does it look still brand new? It probably should since it is not combusting anything in the motor to discolor it.
Is the gap between the arm and the diode to great? Check that by lessening it, tap it against the ground once or twice, it that doesn't work, try it again a few times to be sure.
Set the timing again and then repeat above if all else fails.