Hey Guys - need a little help please !

Did you find this? Measuring from the three holes for the visor/mirror mount, ignore the center hole. My domelight is mounted to the rear rib, The holes are exactly 27 inches back from the visor mount holes. (I should say, the wiring follows the rear rib, so I assume the light mounts there. The light is sitting in a box in my spare bedroom)
They are 1-13/16 apart, so 29/32 either side of the center should have you in the ballpark.
But you're probably already cruising the car around by now.