I'm sorry...apparently I was thinking of the majority of the Challenger radios.
The 7154 was an "oddball" that wasn't even actually a Johnson radio, and it did, in fact, use an EPROM. If I recall, it was a low band radio (30-50 MHz). It was not a very popular radio due to the fact that you had to have a dedicated EPROM programmer for this one radio Many years ago, I worked for a Johnson dealer and even we didn't have a programmer for them!
Here is a link to the Yahoo radio programming group where you can find more information:
Sorry for the error.
Larry