Exeter, the factory manual recommends using the stock 2-1/2" standoffs with their 3/4" wood spacer block. Some people have had concerns with how far forward you have to cut the cowl to clear the cylinder head. I used the 2-1/2" standoffs with 1/2" nylon spacers underneath and was pleased with the results and how the plane flies. If I were doing it again, I'd consider just using the 3" standoffs.

You can search this thread for photos I've posted of the installation.