what combo = decent mileage+ power/torque

How much power are you looking for and whats good mileage for you.

A basicly stock 360 and a overdriven tranny can do very well with simple bolt on's. No cam change at this point in my thinking.

Let me ramble a second here;

I had a '79 Dodge Magnum, heavy late model B body with a 360 and a 904 tranny that got 20 mpg's, mostly stock, upgraded the ignition, dual exhaust off the manifolds and a Carter 625 AFB. Gear ratio was a 2.76 and 26 inch tires.

IF you go a similar route like;

360 with exterior bolt ons,; Smallish carb (600 for example) aluminum dual plane intake, headers into a nice exhaust, (well preped heads would be a plus) bolted to an overdrive 904 version, the 500 will give an overdriven ratio of 2.70 with a 3.91 rear ratio, 2.83 with 4.10's.

The simple bolt ons to a stock 360 and the rear combo will make an excellent daily driver with some guts. Once you start thinking cam, stay small.
You could get the same, if not more mileage out of a set up like this. (Minus the cam change. Still thinking with a stock cam here.) The car is lighter with less of a profile than the big B body.

A stock 360 will produce an easy 240 HP as per how it was rated back then. Freeing up the power of the engine by just simple breathing enhancments should net you a decent amount more.

The mello MoPar create engines, 9.0-1 with a dead cam made 300 HP with exhaust manifolds and a decent exhaust pipe size. Food for thought.