I spent a bit of time marking up the RS10V this evening.
I don't have a particularly good way to do this on a made up guitar, especially one with a carved top, most instructions seem to revolve around building a guitar from scratch and working from a centre line.
The way I've done this so far is to take a long straight edge and extend lines out from the edge of the neck across the body then measure an equal distance from the nut on both sides.
I did this on the RS10V and carefully checked it twice. It looks right by eye but then that doesn't mean much.
Next thing is to drill some small pilot holes and check it all again before drilling the holes out to their final size.