I don't think oil dipstick length is based on engine displacement. The length is more likely different depending on which dipstick location the engine is using, for a front sump or rear sump oil pan. Two of the more common locations are on the block... photos below.
I've got a '55 292 and a '58 312, the oil dipstick on both measures 25 & 1/2 inches from the tip to the top inside of the cap. Both engines have the dipstick tube halfway back on the right hand side of the block for a rear sump pan. (used by pickup trucks & T-birds)
I have two dipsticks for the air-cooled '55 Fordomatic behind the 292. The one in the car has had a minor repair where the cap attaches, it measures 22 & 3/4 inches from the tip to the top inside of the cap. On a shelf is a spare transmission dipstick that didn't need repair, it measures 22 & 5/8 inches tip to top inside of the cap.