Opening up for more questions than answers, but if you are looking for low end torque, I'm curious if you'll see ANY actual increase over stock. Truck motors were built for *low end* torque and meet emissions (key) from the factory, and although the HP numbers aren't that impressive, even the "smogger" 350's were fairly torquey.
I guess the only way to know would be to dyno the thing before/after, or run the stock cam numbers through desktop dyno, then try it with your new cam.
I really kind of doubt the "smog" heads of the 70's up to early 90's are capable of much increased flow with just an intake alone. In my thinking, the heads are the limiting factor (if stock still) not the intake.