The M-90 I believe has different circuitry as it has a 5 program search and the M-80 has no program search..
Now the M-60 and M-80 seem to have the same deck.
BUT: I've seen 2 different M-60 designed decks and yes they were both JW's!
So M-60 has 2 different types of decks just in the M-60JW.
The difference was in the circui board that's on the deck.
I wonder if anyone else has come across this.