Excellent approach, David. With a bit of thought and ingenuity, we can usually work things out, rather than always trying or even demanding to "buy exactly the RIGHT tool" for a job at hand.

The case belling plunger appears to have been either a 5 groove or a 3 groove barrel.

If worse comes to worse, an overized ball bearing and light hammer can be used for belling.

Most brass cases need annealing. My only experience with brass is with Magtec 16 bore brass. They were quite hard as received. The first 10 rounds weren't annealed and took considerably more pressure to bell and crimp than the later loads that I annealed before loading.