From a financial and practical point of view I would get the overdrive and a set of 3.08's or 3.54's first. Used transmissions can be had for $500 and up, and those diffs are everywhere, probably $250 to $500.

For a thousand bucks you will pick up at least 5mpg, and maybe up to 7mpg more.

FWIW, a 488 V10's have been known to get 15, 16mpg so there is no reason a 440 can't do it as well.

All highway mpg I'm quoting, if this is in town use then everything goes out the window.

As many have said, its a juggling act. I'd add that pushing compression too much and getting into pinging/detonation is no fun. With the open chamber iron heads (no quench) I would suggest 9:1 max. If you fit KB quench pad pistons and machine the pad on each hole to get .035 - .040 quench, maybe a bit more. Even with the above it may need premium fuel.

Did OP mention his elevation and is he going to pulling a lot of hills? I would be surprised if 9:1 on pump gas is useful here. Three points I would press, coatings, skirt piston, exhaust port, A Hyd roller, and wait till the EFI is part of the equation, that alone will make more difference then anything mentioned so far and be a lot easier to tune to the edge.

What you need sounds just like the motor I have listed in the engines for sale section.

I did use a liberal amount of themal barrier and dry film lube ooatings in my 440 build. I also spent considerable time dialing in the carb tune and ignition curve.

I didn't go efi or overdrive because the return on investment didn't seem like it would be there. I had gone from a tired old beater with 8 mpg to a freshly rebuilt engine and driveline at 18 mpg .Dumping another 3-4 grand to get into the low 20s didn't seem worth it to me.

Now if you already have a good engine and trans in the vehicle that don't need to be reuilt, then efi and overdrive may be the next logical progression and make more sense.

However, building an engine for a huge, pool table flat torque curve means you have enough torque to overcome the lack of additional gears in the transmission and do not need to build to a narrower rpm range to get good mileage.

I would expect the smaller displacement is coming into play there as well.

Compression makes torque.

I'm currently starting the build of a 10.5/11-to-1 cr 360, with the aim to get very good mileage and decent power.
I settled on a CompCams 20-221-3 (XE256H) cam.

The current daily 318 simply lacks the torque to work the heavy 518 transmission to easily get above 10-11mpg. Most of that comes from the 15-20 minutes commute trips to work and back everyday.
On the highway it manages 15mpg.

I read same art. He used a comp cam hdy. roller kinda big but was in mid 20s on fuel mileage in a car. I kept article but cant find it either, maybe he will we this and help
Might add the cam had some weird numbers for duration.

Another 440 4x4 4.10 axle 3/4-ton build: I put the idea together for a friend.

KB 184 with squish set at 0.040
Measured 9.5:1 compression with the 452 heads.
The above took a little juggling and extra work by the machinist but he seemed to be into it.
Hughes cam HE1423BL.
Perf RPM intake
Can't remember the carb
Headers

Mileage in everyday driving jumped from 8 to 15. The truck would run on midgrade, he didn't want to try regular but it probably would have been OK. This guy was ecstatic, it about doubled his real horsepower, too.

R.