Lean burn to old style ign swap?

You will need to check your carb, to see if you have a "ported" vacuum connection, for the distributor. Most lean burn carbs did not have one. This is required for proper dist operation. You may need to get a earlier year non lean burn carb.
I do agree on the HEI system, over the chrysler.
Carb is a 600 holley with the vacuum port