I'm not quite sure why you mentioned the Pye Pocketfone?, double conversion was the standard technique for NBFM receivers for obvious reasons (lowering the IF makes the modulation a higher percentage of the carrier).Hi cruts,
It would be possible to use a 4046 to demodulate FM in a superhet receiver if the final IF frequency was low enough. In the early 1970s Pye made the "Pockefone" receiver which was a double superhet. The first conversion was down from around 450 Mhz to a first IF of 10.7 Mhz. The second conversion was from 10.7 Mhz down to 100Khz and that was demodulated using a charge pump.