All good advice ... yeah, five seemed tolerable, but 56 pins on the ROMs strike me as extremely troublesome. And as you point out, I may be able to do it with one or two pins, by limiting the initial re-routing.

If I were doing the RAM mod myself I would prefer Tom Lee's method as the new chips are simply soldered to the old and is not only less work than removing the old, but also reversible. I would assume the same principle applies to your method as well in that the new RAM without the Mux board in circuit is undetected, or does the piggy-backing change the equation in yours?