Do you recommend to use some hard rubber under the stand-offs to assist with Vibrations ?

Thanks
Rory

Hi Rory,

No, very few installations are soft mounted like that. Just bolt it through the firewall and put some fender washers on each side to spread the load from vibrations.
I tend to harden the wood around the mounting holes with a few drops of thin CA as well

Most all here do hard mounting. If you need stand-offs, use them directly against the firewall and to the back of the engine.

Rory, The best way to mount an engine to an airframe is a rigid mount. All our radio equipment is designed to survive the vibration if it is installed per the manufacturers' directions. Dan.