I don't have much experience with K-jet/CIS but 48 psi sounds low to me.
I wonder if your distributor could also be plugged, or maybe your filter.
I connected a pump deadheaded to a pressure gauge once and it went to about
135 psi before I could shut it off. Could also be that the grit has polished
the innards of your pump and worn it out.

The 74 that my son-in-law had suffered the same problem, even though it had
been converted to a Holley "Weber clone" carb. It was so gritty that it
plugged the carb about every 50 miles. His car was made in Belgium, BTW,
and while I love the Belgians, this particular car was a lemon in a bunch
of different ways. Maybe got involved in a Flemish/French dispute during
fabrication or something.

If I were you I would take the tank to a shop that will clean it right and
don't give up till you get a filter. RPR in Albany, CA has probably got
one, along with a number of other outfits. Might be good to see about cleaning
the rest of the system and checking availability of a fuel pump also.
--
George Downs, Bartlesville, Oklahoma, Central US