Thx John,

I like to use Hayes mounts as they are lighter than the SIG separate mounts and I can (potentially) swap engines without having to re-drill mount-to-fire-wall holes. I also like to drill-n-tap the mount holes so I don't use nylock lock nuts on the back side of my engine mount bolts. If follows that I don't need a flat "bottom" surface to seat the nuts - though I thoroughly understand the need for a flat bottomed engine mount!