They are both Plymouth carbs somewhere in this list: http://www.thecarburetorshop.com/Carbsaleapplication.htm
I believe I have 2 of one of those numbers and one of one of those numbers on my 3 carb intake. They are Ball and Balls. The only difference physically is the riser from the base has 2 or 3 bolts holding it together. I'm not sure about the internals. They all seem to operate the same. You may want to check with the p15-d24 website. Someone will be able to get the info you need. BloodyKnuckles
Thanks. I have a D6H1 on my '49 Plymouth and have been looking for a mate so I could run a 2x1. There's a D6H2 on ebay and I wanted to be sure they would be compatible before I bid on it. gary