I'd say either one brake ain't biting for whatever reason (as previously mentioned by others) or you have a worn kingpin or tie-rod end on one side. As the brakes grab the drum on the bad side, the slop in the kingpin or tie-rod allows that
wheel to go in a direction different than the good side causing the pull.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission