Nice set of plugs, what's the rod bit sticking out on the plug in the picture to the right. As for the broken lug I would say leave it alone as a bad repair or hint of a repair would devalue the piece. Welding cast iron is difficult to do at the best of times.
The rod was fitted to the base plug in certain late WW1 and post WW1 training grenades. It limits the travel of the striker allowing quick re-cocking. I have a Belgian example with a piece of leather bootlace linking the shoulders to the lever, making sure that didn't stray either.
John
