If I might suggest . . .

. . . a variant of your pressing tool might have been used as a removal tool.

Because these exhuast pipe are available in nested sizes, the next size, or two, down would likely slip over the camshaft journal, under the seal's lip. If you were to splay-out the edge of that pipe externally, it would form a lip which could catch on the underside of the seal, if you had enough "slop" in the pipe to shift back and forth on the cam journal. With a little slide-hammer action, you could remove the seal. If there was not enough slop, you could slice the pipe in half, or less, and that would give you the "slop" that you need.

Just an idea for the next guy.