318 heads

An example of mileage type of camshafts;

High Efficiency Hydraulic Flat Tappet Cam - Chrysler 273-360 245/255
Or
High Energy 206/206 Hydraulic Flat Cam for Chrysler 273-360

But I really suggest calling up a few cam grinders and asking for there help on what would most probably be a better cam for mileage than the ones I listed.