Trans-Dapt wheel spacers

After some fruitful discussions with another FABO member who has the same car body, I am getting a better understanding of the rim backspacing and maximum tire size that will fit under my car. I know for certain that P255/60R15 will just fit if I have a rim with 4.5" backspace.

I would love to put a set of Auto Drag rims from Center Line on my car, with P275/60R15 tires (Cooper) but I will need to use wheel adapters to get adequate spacing to compensate for the 4.875" backspacing of the rim.

Does anybody have any experience (good, bad or otherwise) with the Trans-Dapt 7066 adapters? These bolt onto the 5x4" pattern and migrate to the 5x4.5" pattern with the addition of an inch of space.

Here is the Summit link to the adapters:

http://www.summitracing.com/parts/TRD-7066/