What are they?

[agsolder]

Jedediah North's Tinner's Tool Business, by John H. Demer, published by Early American Industries Association in 1978, has pictures of precisely such tools, identifying them as tinners' swedges, from a catalog published in 1866.
Demer says: "Swedges should not be confused with swages, though their purposes are similar. A swage is a two-part tool that fits into the tinner's bench. To use the swage, the tinner placed the tin between the top and bottom of the swage, and struck the top half with a hammer, imprinting the design. A swedge is a shaping hammer attached to a long pivoting arm, that enables a tinner to quickly and uniformly shape tin. The swedge needed no striking implement, other than the force of the falling hammer." (p.20)
Demer apparently researched the book when he was a fellow for two years at Winterthur.

Here is the illustration I mentioned.