With the two cracks, I'd suggest replacing the entire cup. I repaired a similar hammer (let me re-phrase that: I paid a skilled welder to laser-weld the visible cracks), only to have the crack continue and a piece of the cup to be blown off. I made and fitted a new cup, then had the welder weld it on; it has held up for almost a thousand shots now.

I didn't have to deal with engraving on the hammer; this might be another consideration for Marc. It is a beautiful gun; an unengraved repair would just look "off".

Congrats to Marc, it looks like it would be a great boar-hunting gun!