Better Torque From A 318

Hi! I have been reading this with interest as I have recently bought another Aussie 1973 Valiant Charger 770 with 318 auto, A/C and Steer with 90 thousand KLMS on it (56k miles)This car is absolutely imaculate and the paint is about 90% original and mint! The 318 has a 4 barrel manifold and carby on it but I recently bought a 500 AVS2 for it for a bit more low speed response.
I do not wish to turn this car into a hot rod as I have another 74 charger with 410,5 speed that has about 550hp and runs low elevens.
What I want out of this car is a reliable cruiser with decent fuel economy but with a fair bit of low speed throttle response.
Recently my brother and I went to a car show up the coast doing a round trip of about 400klms and they both got about 21mpg. Yes the 410 with a 3.91 diff and big roller cam used exactly the same amount of fuel as the 318. This means the 410 is much more efficient than the std 318.
This is what I propose to do! The 318 is a 1972 dated engine as our cars had V8s purchased by chrysler Aust in batches usually a year before the build date of the car. This 318 does not have any pollution control as our pollution laws did not take place for a few years later. I think I will pocket port the bowls on the heads and maybe add 360 size intake valves and get a really good 5 angle valve job done and shave the head about .040 to increase the comp. I dont mind spending the money as I paid seventy grand for this car so am looking to put a roller cam and lifters in it but probably only about a 360 type cam as I want a good idle and power from idle but do not need it to rev to the moon.
As it has the std peashooter single exhaust on it I will probably put a single large diameter (2 1/2) free flowing exhaust instead of a twin system . A racer called Peter Brock always used to say on our 308 Holden engines back in the day that a large free flowing single exhaust usually makes more street power than dual exhausts on his 308 engines.
I am looking for your thoughts on a good roller cam profile for this combo?