wild mary- how does that work? what about the crossover section?
I'm sure you know this, but Ross makes double xovers compatible with Gargraves track. Of course, the track spacing is 6", which may be why you are posing the question.
I would lay out 4 #100 and the xover piece (which one?) and see if you can cut enough back on the xover piece enough to make it 4 1/2" oc.