Robert
The dimensions that I used are as follows:
Wood spacer = 1 3/16
aluminum channel mount = 7/8
Engine height = 4 3/4
Total from firewall to prop washer surface = 6 13/16
This build up gave me the 1/8 clearance from the back of the prop to the cowl.

I used a two piece spacer arrangement, wood and aluminum, as I described in my earlier post. The dowel stand off system described by Dick Petit in earlier posts is an easier way to do it, but I prefer a solid continous mounting surface for the engine that the metal channel provides, and I like the shorter mounting screws, although there are more of them. The wood spacer mounts to the firewall into the captive nuts that are factory installed, and the channel bolts to the wood spacer into brass inserts. I offset the channel mounting bolts from the engine mounting bolts so I can remove either piece as an assembly. There are holes drilled into the flange of the aluminum so I can come straight in with a hex key to undo the bolts. The result is a solid engine mount that would be a better protection for the engine if I ever do a "face plant" with the cub. This probably weighs more than the simple dowel stand offs, but I will need nose weight anyway, even with this setup. In another airplane using this arrangement, I was able to mount lead pieces directly to the metal channel to get advantage of a more foward placement. I dont think I will need balance weight on the cub once I install the on board glo system under the fuel tank. I hope this helps. I love this kit
Ric