I have a vague recollection that early SBC distributors had a flat machined to allow oil to one bank or the other. If a distributor without the flat was installed or if the distributor was rotated that bank would run dry. Anyway I think the lifters would run dry and not pump up causing a racket. If you had solids, though and you had plumbed the gauge into the plugged gallery in the manifold you might get an erroneous reading. This might be a wild goose chase with too much poor memory so be aware.
