[bobcowan]

What you've done is create almost a solid motor mount. That's going to transfer a lot of vibration to the frame, and put stress on the head bolt.

Motor movement and torn mounts are a common problem with drag racers; has been for decades. The answer is essentially what you've done, except with a chain and turnbuckle. That allows a little slack for normal movements to prevent excessive vibration. But it will tighten up when under a load and prevent too much movement. Cover the chain with a piece of rubber hose and it will look good and not rattle.