the 557 appears to be a 28 pin version of the 553, so it's probably the same die in the package. I should be able to dump it with my existing rig if I add a socket for it.
And yes, it's really 2048 bytes and not 2000. I don't know why the idiots kept saying 2000 in the data books and data sheets, when it clearly is 2048 on all the dumps I made. The programming manual I saw even re-enforces this lie by saying ROM can only be at 0000-07CF. This is not true at all.