In this order:
1) small tube headers, tuned collectors, expansion chambers, efficient mufflers etc.
2) a good strong 4x4 or RV cam, check CompCams catalog. Valve springs to match. all the lift you can get. You already have 1.7 factory rocker arms. I would stay with stock.
3) hot ignition with a moderate advance curve, vacuum advance mandatory. I like MSD on a 460 like this. Multi spark up to 3000 rpm helps efficiency.
4) intake manifold and carb size is not that important. Stock 4 bbl intake will be fine below 4500 rpm, but a low rpm aftermarket dual plane like Performer (NOT RPM) and a well tuned carb is a help.
5) mild bowl ported stock heads, definitely get the smog bump out and polish the exhaust port.
6) Compression? Geez you are fighting a low compression (8.0 or less) battle without changing pistons. If you accidently stumble into a set of 69-71 429 closed chamber heads, that would help if you can get the quench distance down to a reasonable amount. The pistons are way down in the hole.
I guess the late model 90s truck fuelie set up will be an improvement.
In town cruising mileage can't mean much with 6000 pounds and a 460.
In town gear ratio will make a big difference for acceleration, but kill mileage on the road.
If you get a 3/4 ton truck AOD that would help for any time you can get into OD.
Have a 460 like yours on the stand now, for a lighter car 3800. All torque, 5200 rpm max.
People call me a Ford guy, maybe I am