Further, to give you an idea of the kind of power that can be made with a 400 small block, fairly easily, when a wise combination is put together, simply do a Google search for "406 Chevy."
Chevy High Performance built a fairly basic 406 (small block 400 bored +.030") with a set of iron Vortec heads, Edelbrock Performer RPM Air Gap intake for the Vortec heads, relatively mild hydraulic flat tappet cam, 1-5/8" primary tube headers and a 750 cfm carb and it made something to the tune of 425 horsepower and 525 lb/ft of torque on 91 octane pump gas...both figures under 5000 rpm. IIRC, I think the engine was making somewhere in the vicinity of 470 lb/ft of torque in the 2500 rpm range. That is just about a perfect truck (low rpm grunter/torquer) engine. The only caveat to that being, with the particular combo referenced, the static compression ratio is higher than I'd recommend running (I think it was like 10:1 with those Vortec heads), which would require that premium/91 octane unleaded. Something more to the tune of 9:1 compression ratio would make a little less power but run fine on 87 octane pump gas.