The Banks set-up I have dates back to the mid 80s.
Is there a way to increase boost on those?
Not sure how much boost they put out originally but from what I have been reading I probably wouldn't go higher than 15.
With a 6.9, 6-ish is safe, though I've heard of people pushing 14.
With studs, 15-20 is safe.
12 PSI is basically equivalent to being able to double the power of the motor, assuming you are adding fuel. You increase boost by... adding more fuel(up to a limit). Basically, once you don't have a problem of the heads lifting on you and blowing gaskets, you just crank the pump up and get an EGT gauge. You can then crank the pump down as needed.
Also, when we talk about "cranking the pump up", or the "fuel screw", it's not like a gasser where you change the mixture. It's simply a fuel limiter, which limits the amount of fuel per cylinder/revolution
at wide open throttle. It won't affect 'part load' fuel, because, effectively, the injection pump will always be running the "leanest" mixture that outputs the power you request using the accelerator pedal. If you only attempt to maintain speed(with, say, 1/4 pedal), the pump throttles back fuel as needed to maintain that speed. Add a load(up a hill)? The pump will increase fuel. Down a hill? It'll decrease fuel. Now, there are limits to how much it does this, which is why you can't just use the pedal as a cruise control, but it's 80% like that(Note: The reason it works like this and not as a constant RPM governor is due to the springs inside. With the right springs, it would maintain a constant RPM under 0 to full load at a given throttle position).