Thanks Walter, and yes I'd love to borrow the engine hoist again.
At first we though it was a valvetrain failure because of the clatter when started, but Caveman listened to it when we started it briefly after towing it back to Orillia and he's convinced the bottom let go.
I'm looking into JDM engines to swap in and asking if Gord Bush would diagnose the failure. In my mind it was built for this stuff, but JoeT and STeveD think it's oil starvation.
I had my biggest tune on it (17psi +/-1psi), but I wasn't flogging it mercilessly around the track like a Hooligan!