Correct. Morecambe was still a manual exchange until late 1974 and manual exchanges used A/B boxes. The grey STD payphones (Box Coin Collecting 705 in kiosks
http://britishtelephones.com/bcc700.htm) were only introduced when an exchange was converted to STD working. The change of telephone happened just after the conversion as the STD payphones needed equipment in the exchange to enable them to function (Coin and Fee Checking relay sets).
That is why if you have one of these telephones, it will only work as a normal telephone and will not open the slots or give the 'pips' unless like some of us, you have a former GPO exchange still fitted with the relay sets.
There were still exchanges without STD working after March 1978 - several in Wales and Northern Ireland. The PO's annual 'List of Exchanges' giving info about each exchange no longer listed whether an exchange had STD after 1978 as they all had it by 1979 - except for the one manual phone left on the Isle of Lewis.