Ed - The "D" indicates it is equipped for 5,000 ft altitude. Uncertain what THAT means - but it's probably slightly higher compression pistons and a different carb orifice calibration.
My guess is your hood came off a distillate H or Super H.
Incidentally I own a pair of '53 Super H with the DJ code. How it wound up here in western NY (maximum altitude ~1,500 feet) is a mystery.