340/360 is the gold standard Performance small block. now all that aside, it seems the OP wants to do this with a 318, he mentioned low RPM and torque.
I think I would do this in this order.
1. Dual exhaust
2. rear gears
3. 4 barrel (with stock cam)
4. cam shaft swap
i would do these things ona at a time then test/tune and measure improvement.
I would go no further and spend no more than this if it came to heads and pistons I'd swap in a 340/360 or a magnum . again my $.02 and I'm sure I'm wrong to someone with more time and $$$ to invest in a 318.
