Just curious? did you have oil restrictors in the block when you had over 300 passes on the motor before the rebuild? I'm not saying that you're not pumping out 1 1/2 qts. on a hard shutdown, but i am leaning toward not enough clearance on the bearings. If you had restrictors before why didn't you reinstall them before installing the motor. I've never had this happen before, and i have a Dart L' "M" block built 434" but haven't installed it yet. I'm watch this thread very carefully, i cannot afford this to happen too me. All i have is an 8qt. pan and a high performance Moroso oil pump.
Also you didn't say what kind of rods and what bolts, did a bolt break, did a rod break. I'm still curious about where it started, except you said a main bearing went dry.
Zip.