Quick question, you all run SORRCA rules?
Quick answer Chris....yes and no. I would say the majority of us follow the rules laid out as a general guideline. However we have never given/figured points for anything on the scale side, are club has more of a run-what-you-brung mentality. Besides Goat Hill, our scale gtg's are more for fun then anything, and at GH we simply break it down to 2.2 and 1.9 tire size to keep it fairly even capability wise (and only compete against the clock).
If you want to go 1.55 tire size do it..."thumbsup". Its really whatever you think looks and works best. Will say that 1.5 can be more challenging (you lose a lot of ground clearance at the pumpkin) then the bigger tires, but they do "look right" if your really going for true scale. Its really up to you and what your "vision" is....and have fun.