I am thinking of something similar, but rather than a wide, flat shape, I'll try to use part of a 3" round axle (which I think is 4140) welded to the top of a piece of 3.5" round stock about 19 inches long (was a counterweight for something). I'll try to replicate Charlie's anvil base with the round tube filled with gravel, and three forged steel wedges as tightening pins.