RE: fpe 5.8 with the shakes...
Yes, What the engine is bolted to makes a HUGE difference. Even small singles vibrate badly if mounted to a steel mount, or a mount clamped in a vise. Try this at home. Run your plane with, and without the wings. Without the wings it will vibrate more than you can imagine. I taxied my Brison 3.2 for two tanks without the wings on. The tail shook so badly, it broke the outer Robart hinges on the horizontal stabilizer. Thought I had a serious problem. Called Brison, they told me to bolt up the wings. The difference was unbelievable. Now smoooooth as silk. Waaay cool, now.