I can tell you a Vortec 305 will pull very nicely. We just put some 059 305 vortec heads on the Crane 272H10 cammed 312 in my brothers 1980 C10. His Q-Jets secondary cam disintegrated a couple of weeks ago. To get the truck mobile we blocked the secondary air valves closed and he had been driving around on the primaries. Even running around on the functional equivalent of a DualJet ~350 cfm @ 3.0 in/hg the truck pulls hard past 5,500 rpm.