Bob,

I made a end grain balsa ply sandwich spacer 7/8" thick which the 3 stand-offs mount to. The spacer is epoxied to the firewall. My intent using this end grain balsa/ply sandwich is to help dampen engine vibration. We'll see how well it works. I started on the pipe tunnel, but have not yet glued in the 1/16" balsa as the replacement for the fiberglass tunnel as you did. I have to make it fit properly. The fit and finish of my airplane is average. Nothing to brag about. I'll keep you posted. Thanks for all your help.