440 what am I missing here?

A few things add up.
Single plane intake ( high rpm)
Low gears NG
That cam ( high rpm)
Exhaust manifolds NG
That is an Awesome truck.!!
Should roast the tires.
Have to get things to work together
You either build a low end torque monster set up ( preferred for street )
Or
A high rpm motor ( drag )
Settle on the true use , then build towards that.
following.....
Best of luck !