Thanks for the advice. I was starting to think about the block being loose and what all could happen. I think I'll try putting a temporary plate in this weekend just to keep it from flying out while I gather the spring swap parts. My main worry is that the ubolts aren't actually all that tight now that the block has squashed down over the perch. That too would make the block more likely to spit out as you say.

Ironically the whole reason for the spring swap was due to what felt like huge axle wrap. It may have been the block weirdness.

Looks like I"m taking the car today. :-)