[olddog]

It sounds like you like the mild manors of the cam. If it is flat tappet, changing out to a roller cam will give you greater ramp rates, which gets the valves open sooner and keeps them open a little later, at the same durration, thus better breathing. More lift will help too. Depending on the lobe center line, you may be able to go with a little more durration without hurting the idle. Valve to piston clearance would have to be checked.

I would say a good set of aluminum heads will do a lot for your engine. From published data that I have seen about 1.25 lb-ft of torque per cubic inch of displacement is about a good as you will get normally asperated and still have reasonable monors at the low range. Which would say 440 torque is about as good as your going to get, and you are likely to be in the 380 range now. To get there you need real good heads with a cam matched up. For low rpm you do not want to go too large on the ports.

You didn't say if the intake is single or dual plane. I think a good dual plane would best suit what you want.

The quickest and cheapest kick in the pants would be to switch the rocker arms to a 1.7:1 ratio roller rocker set. Valve clearance would have to be checked. If you are not wanting to change the heads and cam, this would be my choice.