Here again I am definitly not an expert.I have found however that gearing seems to mean everything as far as MPG is concerned,and yes you need a well tuned engine to drive those gears.In my 55 2nd I have a rebuilt 350 Chevy truck engine,(circa 1974)plus a 700R4 trans.going to the stock 3:90 rear.It gets me 20 MPG all day long as long as I drive it carefully.This includes city as well as highway miles.The OD trans.seems to be the secret to better mileage,however you have to have enough power to push the vehicle.A 3 speed auto,or a 3 or 4 speed manual trans will turn 1 to 1 to the rear,whereas an OD trans will go at about .78 to 1 final drive.You should be able to use a regular manual,or 3 sp.auto.and use a rearend geared about 3.08 and get decent mileage as well.It all boils down to how many RPMS you are turning at cruising speed.My findings are strictly on a trial and error basis.
