Obviously the problem is that we're too high tech for our own good. Those Speedway Engineering engine mounts we used were designed for a flathead Ford, like that rusty hunk of crap above. One important detail we overlooked, though, was that silver band around the flathead mount.
Our mounts didn't have that band, and since they're hollowed out on the bottom, the mount can sag as the rubber spreads under the weight of the engine. Yes, even the featherweight Hayabusa engine was making the flathead Ford mounts sag. Surprised the hell out of us too…
The simple solution would be to weld a ring to the plate the engine mount sits on, preventing the mount from spreading. But since the car was sitting in a welder inaccessible driveway, another solution was needed. I hacksawed off the bead-rolled end of a scrap piece of 3″ aluminum intercooler piping, cut 16 slits in it, and bent the resulting tabs inward with a pair of pliers.
This pres-on ring fits on the mount, and since the mount sits on the folded-in lip, there's no way for the ring to slip off. Of course, since the tube was 3″ OD, and the mount was also 3″, there was a bit of squeezing required to get the rubber into the ring. I soaked the mount in soapy boiling water to soften it up and lubricate it, then compressed it with a T-bolt hose clamp and pressed it into the retainer with the vice.
Nothing is ever simple.
The actual interference between the engine and subframe was just on the corner of this bolt head. Just to be safe, we decided to make more room.
A simple wood countersink bit works just fine in aluminum.