What's the absolute maximum range of your Duster?

No, I'm trying to keep it all original, but I know a lock up would probably help. Thanks.

No problem. Then as I said earlier, I do believe that a retuning of the carb & distributor for Max Benefit in the mileage seeking would be where to start with a recurve of the distributor and then a fine tuning of the carb. Tweak tweak tweak!!!!

Best of luck in the search!