I love these fuel mileage threads...I have a nice and tough as nails 65 3/4 ton with the 352...single digit fuel mileage last I checked...I didnt buy it for fuel mileage...I bought it for hauling ability and the trucks particular sentiment...fuel mileage wasnt a consideration...If one wants a truck with decent fuel economy...get a later model Ranger...of which I have one thats been very faithful to me and is still moving along 275K later...or a 70's Courier...the Rangers predecesor...
As far as the FE engine differences...another thing I get a good chuckle out of when people compare the 390 to the 352...as Bill said, virtually identical...only the rotating assy is different...
Anyway, keep the 352 a 352...nothing gained by punching it out except a lighter wallet....which to me is the best reason to keep it stock...keep the wallet as heavy as possible :-)



- cs65