Daily driver small block build

Whatever you do, the quickest way to lose cylinder pressure is with a wide LSA cam, and with the loss of pressure, goes the fuel economy.
Oh sure, you can get away with using the stock Magnum cam but look where the factory installed it!
If yur serious about fuel-economy, you need cylinder pressure. And if yur going that route, yur doing pistons. And then it don't matter anymore as to LA or Magnum.
The easiest engine to get pressure with, when doing flat-tops, has the most swept volume, and the tiniest closed chambers, so you might as well marry the Magnum heads to whatever flavor 360 cubes; then pump the Dcr up to around 9.0. Good luck running that with iron heads. even on best gas. and forget the stock Magnum cam.
So
at this level you are looking at Pistons, boring, decking, a crank rebalance; plus alloy heads, a cam kit, an induction set-up, and an ignition system, and yes headers and a free-flowing exhaust system.
So basically, from the 360/5.9, all you will be reusing is the engine block, the rebalanced crank, maybe the rods, and the various covers..
You might as well call up one of the vendors, and just order up what you want, and have it done right in the first place,
And that's
AJs Opinion.

Or
you can do just slam some tall crown pistons, like KB107s into a 360/5.9, which sometimes come in at .012 below deck on an LA, that with an .028 gasket and closed-chamber ALLOY heads will get you a nice decent quench, a nice Dcr potential, and
Then you can reuse the oddball Magnum cam and time it just about anywhere you need to, to get the pressure DOWN to 87 gas, which will then get you a buncha power duration, to really suck the energy out of the hot gasses. With this combo headers are optional, cuz there is not gonna be much effective overlap to speak of. But, you still need a free-flowing dual exhaust. Even without EFI, this might go into the mid to high 20s mpg, if not, an overdrive will get you close to 30. IDK how much power it will make, and don't care, cuz the low-rpm torque will be ridiculously much fun. Run it with any gears/any stall/ and wipe that sillygrin off your face. lol.
The only thing that could make it better would be the 1-2-3 combination of deeper gears, overdrive, and a LU convertor .... like
3.73s/A518LU/65=2130rpm; with a starter-gear of 9.14 or
3.23s/A500LU/65=1840rpm; with a starter-gear of 8.85
both with 26.5" tires.
Or if you like to row gears, how about the Commando 4-speed with a GVod behind it, and 3.23s, for 65= 2040 and a starter of 9.98
Course if you have this hi-torque 360, you could probably get away with the A833od (3+1) and 3.23s, for 65=1950 and a starter of 9.98. Second gear is a lil shy at 5.39 but for a DD should work out Ok, cuz with it, 35mph is a nice 2400 rpm.