The two radios I'm referring to are exactly the same save for two differences: The '54/'55 version has black push buttons and the small "Emergency Broadcast" symbols on the dial face glass. Other than that, they are the same. Some of the early '51 Kaisers (including the early Special I have) used the six push button '49/'50 style radio and that one definitely required that the firewall be altered in order to fit. The later '51 Ks do not have this modification so the '49/'50 style radio can only be fitted in the early '51s. Here's pictures of the '51 - '53 style and the '54 - '55 style. They are the same inside and outside dimensions are the same so they should be interchangeable. Perhaps a dealer did that?