[G8BBZ]

Just a note regarding the Redifon R408 Receiver.
I don't believe this receiver had an ISB capability as it was really a dedicated Ship's Main Receiver - though many did find their way into non-marine applications I think. Though SSB capability had been introduced as a mandatory requirement for larger vessels, the bulk of marine radio traffic was still handled using CW at this stage.
In addition to Marconi Marine, the receiver was also sold by Hagenuk of Germany - badged Hagenuk - and found its way into many other marine radio installations by a variety of companies.
The receiver uses primarily silicon transistors - the first Redifon solid state receiver to do so - and was streets ahead of rivals such as the Racal RA217 which used Germanium devices. It also featured variable IF bandwidth - based on the "sliding doors" arrangement - which was very popular with operators and is very pleasant to use.
The receiver was very successful, particularly in the marine market where it became the de facto standard in Europe. It is surprising that so few seem to have survived into private hands.