These older transmitter and receivers do not use a link or anything like that. They are old school... They have various Mhz bands that they are made to work within and channels within those bands typically using crystal sets or a synthesized frequency. Many are also available in AM or FM radio types ( the ones you mentioned, are FM types ). Because of all of that, the electronics also require that they are tuned for those so they work properly.
So the R700 you listed is using the 35 Mhz frequency... look to see if it also lists the channel it is setup for. The transmitter must also be using the same as the receiver ( or visa versa ) in order that it is compatible. To change the frequency and channels, in the old days you'd send the transmitter and/or receiver into the manufacturer or a properly licensed radio technician to change these and then tune them to work within the new frequency and channel. I suspect the labor charge you'd be charged would exceed the value of the set.