I believe the Mousehole anvil pic you posted was made prior to, 1820 as, that's when they started adding pritchel holes.
Also I wouldn't be as worried about the "sweet spot", as I would be that the edges are so radiused, and you'll need somthing square, to make weld scarfs, necking down, etc.
I have a PW with chipped edges that I going to weld up and grind square.