Could the bike have been built using a newer frame ?
That is entirely possible, however....
1955-56 are CONFIRMED model years for these bikes. I have heard 1957 was a model year by only a couple of people through the grapevine, with no concrete, credible sources to back it up. Not even a catalog ad, and I think I even started a thread on this very subject.
The problem is, 1956 models are remarkably scarce. I have yet to see one in person, only photographs. The different tank graphics, while original, could mean 1956 or later. ALL other graphics from 1955 carried over into 1956. 1956 models also were equipped with a spring-loaded carrier in the front and the headlight was moved from the fender to the handlebars.
Also, by 1960, Huffman had completely switched to cantilever frames. The tank for a Radiobike will not fit on those frames at all and it would be obvious if the tank was butchered. Unless the tanks changed to fit those cantilever frames and I am unaware of it. Bear in mind, the radio chassis would also be different because there would be much less space inside the tank if on a cantilever frame.
The only other thing I need is a photo of the mounting area for the rack, behind the seat post. That would definitely give it away. It should be a single bolt, through a small tube welded behind the seat tube. I have noticed the Radiobike rack is the only rack by Huffman during this period to mount right there. All others mounted with a bolt through two tabs against the seat post clamp.
The condition does not make me suspicious, nice Radiobikes have surfaced and those tank decals are not reproduced. The earlier ones are reproduced by MLC.