All FM transmitters legal?
Not all FMs are narrow band. The ones with the gold sticker have been converted ( more than likely).
The reciever must also be narrow band. If the radio is that old I would send it in to be checked out anyway. They can tell you for sure if it's narrow band. If you use this transmitter before you know if it's narrow,take the Freq. pin for the channel above and below it also. I have an FM made in 1990 that is not narrow. Back then when you sent it to Futaba to be upgraded they put a gold sticker on it with the date showing it was converted.
Two radios on the same channel can not be used at the same time. Dosn't matter if one is AM one is FM or one is PCM. There will be interference.
hope this helps, later daveo