I've reading some the derogatory posts that referring to the FE engine series, in generalized terms such as " they're old technology POS". The reality is far different. They were actually excellent power sources for everything from Mustangs to F500s. The gas price in the early '60s was about 25 cents/gal. but drivers were still looking for economy. My dad kept track of the MPGs on the 5000lb. '63 Country Squire with a 2bbl 390, and tuned it up when it got below 15 around town. My '66 428PI with nearly 400 HP got nearly that with 17 MPGs doing 75 and I was lead foot kid on the edge of loosing my license. The emission laws were the death of FEs, not out dated design. The 351-400M engines that replaced the FEs were never an improvement. To get 5.6 MPGs in a 2500 lb. CJ5, something besides the engine choice, is going on.