Robert
I am away from home right now, back Saturday, so I cant give you measurements yet. The total distance was close to what the instructions said was needed, I followed the suggested method to set the final dimensions. What I did was to mount the engine on a aluminum channel, about 1 inch high, and then bolt the channel to wooden spacers cut to size to make up the rest of the distance needed. I made 4 separate blocks, 2 horizontal and two vertical The wooden spacers were cut from a piece of pine board and sealed with epoxy. The wooden parts have thru holes and are bolted to the firewall using the captive nuts that are already on the firewall. The aluminum channel is bolted to the wooden spacers using threaded brass inserts in the wood. The engine is bolted to the channel using locknuts. When I get back I can take some pics to show the detail. I used #10-32 SS hardware for all. The channel I bought at Home Depot. I used this method successfully on many airplanes. It avoids having to use a single large wooden spacer that may split, and every thing is removable from the firewall in case the engine is replaced by some other size
Ric.