@str12-340 since you didn’t give a reference to what cam you’re currently running (beyond an rpm range) and it seems all you want is a new cam, here is where I’d start as a recommendation.
https://www.compcams.com/xtreme-energy-206-212-hydraulic-flat-cam-for-chrysler-273-360.html
I think in a 8.5:1 318 with overdrive and tall gears, (and if you let me get rid of the avs2 carb and tune a Holley VS for it) I could get reasonable mileage with it. I think 18-25mpg is not too far fetched.