I have restored many Buick radios over the years and the 54/55 selectronics are identical in every way except for the dial equipment. The colors are different in 55 as opposed to 54 and the 54. Otherwise only the model number really sets them apart.
The selectronics only came in one model number each year in 54/55, there are no variations per car series. There were only 2 radios offered for both years, manual and selectronic. Personally I don't like selectronics since you cannot store presets in them (they did the right thing in 57/58 by introducing BOTH features in the selectronic models).
54 Buick Special 41D (With a 1956 Century engine!)
64 Fiat 1500 cabriolet
83 Bertone X1/9
84 Jag S3 XJ6