I wouldn't rip up a rare radio to convert it to solid state, but the FM board is a reversible modification that taps into the AM tube circuitry before the audio amplifier. FM reception requires significantly more than the 5 tubes it takes for the AM radio to work, so you can't just convert the AM circuitry to work on FM.
The '54 factory radios are very scarce because they were only made for 1.5 years.
