I hope this isn’t repeating a thread; I haven’t been a moparts regular for a long time.
Ok, so after a lifetime of using old Mopars for my daily driver to this very day, I realize that I’ll simply never be able to drive a Neon, Civic, Economy Car X or anything else as hard as I’ve tried. That said, funding fuel for old Mopars for the daily drive makes less sense as time passes and prices rise.

I’d like thoughts on these combination ideas for running old iron as efficiently as possible without going for a /6 Valiant (nothing wrong with that, it’s just not my thing right now).
Here's my answer to keeping my pride and my sanity without breaking the bank too badly on the car, the modifications, or the gas bill. Let me know what you think.

A “lightweight” B-body; (1966 Coronet 2-door with nothing but A/C for options)

Original 90,000 mile 273 in great shape (read, I’m NOT rebuilding the engine).

Modern Magnum heads on the LA engine; yes I know these require different lifters and pushrods, have different valve covers and need the Mopar Performance intake with the vertical bolts I’d obviously use the dual plane.

Dual exhaust (for better or worse, you gotta have it) thru the cast iron manifolds. I understand that headers are more efficient but need a richer mixture; I would use a little 2-bbl hydraulic cam (original 2-bbl ‘66 273 has solid lifters -right?) If the small cam and magnum heads would allow for headers without running rich, then I’d run them, but the idea here is staying in an old ride with a little small block rumble but best economy, not high performance (read, my objective is not performance here and I’m ok with that, I have a 383 Charger that goes fast just fine). What do you think headers would do for mileage?

I’d stick with the original trans and converter, works like a champ, and also keep the 2.76 gears.
Electronic ignition, new plugs, wires, perhaps a K&N filter element.

What carburetor? obviously a small 4-bbl with a choke that can be set up to run well on a non-performance application, obviously something that’ll run well a little bit on the lean side. I was thinking maybe a Street Demon if for no other reason than I hear tech support is outstanding.

Add electronic ignition, keep the tires inflated, (225/70R15s on 15x7 steel rims from an 88 5th avenue with dog dish) and use good low friction fluids in the trans and rear.

Since it’s a daily-daily, I was also considering getting the classic air A/C setup rather then messing with the original system. That should help out in the weight dept and also be a ton less parasitic power loss.

I do realize that the expense I go to here will mean it takes a while to realize any savings, but I’m ok with that. I figure as it sits, driven conservatively, the car should get about 14 and 22 MPG. I was thinking that the above mods might bump that up to maybe 16 and 26 mostly by leaner 4-bbl primary jetting, better heads, duals, and electronic ignition.

Am I smoking dope or am I in the ballpark? Remember, daily efficiency and reliability is the goal, NOT performance. As long as it’ll downshift and I can get a little kick from the secondaries, I’m good with it.