Ok, half inch plate and half inch spacers. That's exactly what I need to center the caliper on the rotor in my case as well. I only need to get the calipers in hand and do just the same as you and get the proper position in relation to the rotor surface.

The trick for getting the positioning is just what I was looking for.
Soon as I get the calipers here I'll get the steel and get to work.

the difference in braking from an 11.3 inch rotor to a 13 has got to be huge. That car has got to stop great!