That would be a fun build. If not mistaken, at one point early on I think the 1377 had a magnet on the probe to shoot bb's. Think it was a rear-cocking model, similar to the Medalist 1322. Wasn't much into airguns then, so I could be wrong.
Do we need a bb gate?Yes absolutely, imho. Handling/shooting bbs is different from lead pellets. So, keeping that knowledge/experience together must surely be a good thing.