I'm currently going thru this exact subject on my Mopar's. I started with the 74 440ci Ramcharger as it's only getting 6.6mpg, next I'll work on the Duster 360.
I also started a thread on RamchargerCentral to document my steps and before/after mileage for tuning the timing/vacuum advance
Vacuum Advance Timing for Maximum Efficiency
Same exact methods in the Mopar Performance engine books for fifty years. All anyone has to do is READ.
Thanks for posting, btw. Maybe in video format, it might reach more people. Especially since the MP books are getting impossible to find.