I agree with Dick about the longer standoffs being an issue with twisting forces. The longer ones have to be transferring a twisting force to the firewall due to basic physics. Engines and propellers provide a source of torque, and that motion is transferred to the standoffs, with the longer ones magnifying (leveraging) that twisting force. With a little bit of thought and easy design work, twisting of the motor mounts and excessive vibration becomes a non issue. Simply put, using a motor mount designed from wood, lightened to eliminate unneccesary weight, but still providing a solid "foot" that pairs engine mounting bolts with the firewall, effectively transfers engine pulses and eliminates vibration.

I've never purchased an after market metal standoff or used aluminum/metal post supports to hang an engine and have never experienced the high vibration issues others seem to have. Perhaps that due to the wood motor mounts used. Don't know for sure, but that's about the only differences I've seen between my installations and others. My planes stay together just fine for a couple of years or until I sell them or crash them. Never had one shaken apart to date.