1969 440 cars were designed to have 5/16" fuel lines and 1/4" vapor return for original equipment. Any that came through with 3/8" were a mistake and do not meet the OE specifications. Unless you are the original owner of an unrestored car, you can't assume that it is original. Even if you have 440 cars or heard (this is called heresay) of others with 3/8" lines, based on the input you are getting here, I would not draw a conclusion that all 440's came with 3/8" lines. 5/16" is correct for 440's...honest!