I think 14 MPG is decent.

I ran a '70E about 4,000 miles in 10 days a couple of years ago. From IL to CA and back over the Rockies. 14 MPG running 75-80 ish. Engine is a 496B with warm cam. EFI, .81 OD TKO, 3.23 rear and ~25" tires. At light cruise running around 50 degrees advance and a little lean on the AF. One tuning challenge was when to dial back advance and richen the mixture for moderate acceleration w/o rattle. WOT is pretty easy to tune. I would likely have gotten 15+ MPG with taller OD which the engine could eaisly handle at cruising speed... but like the shorter OD as a top end track gear.

My understanding, the 6 pack can do quite well with careful tuning of the center carb and plenty of vacuum advance (50+ degrees?). Just a little easier to get there with EFI. Also, EFI handles altitude, temp and fuel changes w/o penalty which matters a lot in the mountains.