myself,
I say pull the distubutor and drive gear.
Use a drill to run the pump ( don' forget CCW on a BB)]
IF you are building pressure the drill motor will let you know via resistance.
If so, and no pressure registering,
Change the guage,
Still no pressure ?
change the filter and repeat.

I would NOT START THE MOTOR AGAIN until the drill motor produces pressure PERIOD!!

please report back an whether it was a filter problem or not. AGAIN,
I would NOT START THE MOTOR AGAIN until the drill motor produces pressure PERIOD!!