I would check the fit of the cork oil pan seal. It shifting during assembly, or missing altogether, could explain the dry test run and the splurge once tilted back. Remedy would only entail the sump off.
To check the oil gallery end bolt, take out the rearmost side gallery bolt and fiddle a wire towards the back. If the bolt is missing (which I doubt because Dick M. has a point) the wire will eventually scratch at the flywheel.