Engine Trans Axle

I have just purchased a 1968 Camaro, without an engine or transmission. The rearend is a 10 bolt with strange axles and gears, I roatated the tires and got a little over 4 to 1 ratio. I am guessing this is a 4.11 setup. My question is....What engine/trans setup will get me the best fuel economy, using used or remanufactured parts. My car was originally manual but was converted to auto. I am leaning towards a manual trans for overdrive purposes. Is this the harder way to go with crossmember and axle length issues? I want to use this car as a daily driver and trips so I want it to be setup for low rpms at cruising speeds (30/ 55/ 75) Any info would be great on matching of parts. Thanks

well, first things first, if you are concerned with highway fuel economy, those 4.11 gears are gonna have to go. Those are drag racing gears. For econimy, youll want a small displacement small block chevy, backed by an overdrive transmission either manual or auto, and no higher than 3.45 gears. i suggest 3.08 if your making a highway cruiser. My 2.73 gears are great for the highway, but are rather anemic at acceleration. the 3.08 will give great highway cruising speed, but still be fun at the stoplights.