[Arran]

The biggest issue is going to be finding an original Philco speaker as a replacement, the tubes are fairly simple enough though shouldered versions of 6A8s, 6K7, and 6Q7s are harder to find then the metal and tubular types. Fortunately, unlike the 1938 models metal and glass tubular types will fit into the tube shield bases they used in the 1937 models.
The bullet styled cabinets are fairly collectable, though the cheaper versions used a faux wood grain on the front panel, so that is something to look out for, if it's messed up that will detract from the value. You can work around the original 8'' Philco speaker being missing, but I would try to pay as little as possible for any set with it gone, on some of those the bolt pattern is different from a normal 8'' pincushion style. Aside from that you will need a replacement for the field coil of the original speaker, so it will need either a filter choke or a resistor with two filter caps that are of a larger value then the originals.
Regards
Arran