Don, I think you're worrying needlessly. Use the 1.5 rockers and fire it. For initial start-up and cam break-in, you want as little pressure on the lobes as possible and the 1.6 rockers would increase the pressure by squeezing the springs tighter. Change to the 1.6 rockers later after you have 200-300 miles on the motor if you want to.

Worst case scenario on the deck height is that the pistons are in the hole about 0.035" which would yield a c.r. of 8.65 with 7 cc's in the eyebrows and an 0.039" gasket. Your engine builder should have a record of the deck height.

Anyway, like I said, don't worry about it. The motor will make plenty of torque just off-idle to pull that lightweight little roadster. The cam you're using is just one notch off bone-stock and Chevy built millions of motors like this with excessive piston-head clearance and low static c.r. It's gonna be smooth as silk and pull hard.