The Idea!!!!

Mostly stock 318 with that OD transmission would be my choice. They easily got in the mid-20s MPGs back in the day. You could put on EFI, and electronic ignition, headers, good exhaust system, and you might hit 30 MPG on the highway if you take it easy. 4 or 5 speed automatic with computerized lock-up converter maybe? And it would still be pretty peppy around town.