If you have an original '41 radiator, you do not want to use anything above a "zero" cap. The design of this style of radiator cannot handle the pressure. I seriously doubt that a two-seal "zero" cap exists. Maybe you could alter a 4# cap to vent at one pound, but I don't know if a 4# cap will even fit on a '41 radiator.
Carl

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