Here's the 1943 "Fits, Tolerances, and Wear Limits" publication I've been using for my270. It lists the clearance at bottom of piston skirt to be .00375"
Could be they updated the size by the time of the 1950s publication or there may be a difference between the dome top WWII pistons and the flat top later pistons. At any rate, the difference is only .0005" so I don't think I'm going to worry about it.
