Those early emissions years, especially around '73, they were really doing a balancing act with compression, timing and fuel.

The Dodge FSM actually has two 400 cid specs. I missed the second one before. The other has timing start aroun 7.5 BTC. Not terrible but you can experiment with 10*. That's within the tweaking expected.

IMO the one emission trick that really hurt throttle response are the timing delay systems. One was called OSAC - Orifice Spark Advance Control.
Not every engine had them. But if yours does, learn how it works and then take it of action so there's no delay.

A pretty complete list of Master Tech is here
http://www.imperialclub.org/Repair/Lit/Master/index.htm

TSBs here
http://www.hamtramck-historical.com/library.shtml