42 was the original class 60 (C-16) so the boilers should have swapped easily. Remember that Baldwin built virtually all of the class 60 locos, and the ones that Grant built were built to basically the same plans.
So far as Baldwin locomotives go, many of the engines in the various Baldwin classes had interchangeable parts and Baldwin made them that way on purpose. They had standard design boilers, cylinders and frames. You could put them together many different ways and get different locomotives, but many of the components would still be the same and would interchange with other BLW engines. A Baldwin class 10-32-D 4-6-0, or 10-32 1/4- D 2-6-2, or 10-32-E 2-8-0 all had the same size cylinders, and could use the same boiler as well, as use many other components, for instance.