The knob and escutcheon could be swapped, but I really doubt it. The different ion traps indicate that there are definitely electrical differences between the two chassis. You see, the ion trap on the 1948 is an electromagnetic type which I recognize by its pole pieces and the type of thumbscrews as being the same type that was on my 721TS. This ion trap, instead of having a permanent magnet, has a pair of coils (located on the underside) which connect to the power supply via two wires. The bleeder network in the power supply must therefore provide via additional resistors and/or value variations some means to compensate for the absence of the ion trap's field coils from the circuit of the 1948-1/2. I suspect, although I haven't actually seen the speaker of either set, that there is a field coil on the 1948's speaker and a PM speaker in the 1948-1/2 which would have no field coil and require the addition of a filter choke and/or resistor to maintain proper filtering. As for an explanation of the variation, I suspect that the first production run of 8TS30's (the 1948's) contained leftover 630TS chassis which used electrodynamic (field coil) speakers and electromagnetic ion traps. Later productions may have contained a chassis designed specifically for the 8TS30 which was modified to operate with a PM speaker and PM ion trap. I also believe that the design which was licensed to companies such as AirCastle, Crosley, Fada, etc. was actually the later variation (8TS30) chassis. I own a Crosley 9-408 and Fada TV30 which support this theory since both sets use PM speakers and PM ion traps. Both sets feature the same 13-channel tuner and the black-on-gold escutcheon, but the actual selector and fine tuning knobs differ between the two sets. The Crosley's selector knob does not look line any RCA knob I've seen, while the Fada's selector appears to be like the knob on the 721TS except that the Fada's knob is painted gold to simulate a brass finish. Photos of the 721TS which I recently restored and sold can be viewed in the vintage b/w forum with more pictures and info about the 721TS and the Crosley 9-408 located at
http://home.earthlink.net/~amptechsys/serv03.htm
John