I think I fixed my lever-drop issue.

Removed the small pin holding the latch..and removed the latch and spring. The hole in the end of the lever is pretty deep..and the spring really isn't compressed to any great degree to tension the latch. They could've used a somewhat longer spring..or drilled the hole less deep for the spring Uberti did use.

I made a 3/16" long plug out of some appropriate diameter brass rod and dropped it into the hole in the loading lever. Fitted the spring and latch back in..and re-pinned it in place. Got lots of tension on the latch now..substantialy more than it had. Still easy enough to unlatch for use..and I'm hopeful the lever will stay latched up.

The notched lug on the barrel isn't all that deeply notched..If I have further issues I may file the lug notch a bit deeper. However I'm confident the lever will stay in place now. Only shooting will tell for sure.