First, we'd limit your max rpm to 6,000. You didn't mention if you replaced the rod bolts on your build. With the piston speeds the 3.75-inch stroke produces and the weight of those TRW forged slugs, spinning the engine past 6,000 is looking for trouble. With the cam and heads you're running, going past 6,000 would be a waste of time anyway. You need to move your truck on torque.
Swapping to the RPM on your 388 will give you a good boost in horsepower and torque. You'll see around 15 hp over the standard PN 2101 Performer. The torque will follow suit with a smaller gain. The peak horsepower should go up around 300-400 rpm. As for the stock stamped steel rockers, they work pretty well for what they are. They're very lightweight, which helps valvetrain stability. Roller rockers really wouldn't give you more power sticking with the stock 1.5:1 ratio. Unfortunately, we haven't had much luck running higher ratio rockers on the Xtreme Energy profiles. The Xtreme lobes are so quick that when you increase the rocker ratio you can run into high-speed valvetrain stability problems. Going to a true roller rocker will put less stress on the valveguides and usually have better off-seat ratio based on the design of the rocker.
You asked if full-length headers would be a benefit. A benefit over what? Are you running stock exhaust manifolds or shorty headers? If you're running stock-type manifolds, yes, you'll see a big gain in performance. On this engine, you could see gains of 30 lb-ft of torque and well over 20 hp. If you currently have shorty headers, you'll see some of that torque boost but very little horsepower increase.
Finally, we'd swap out your stock converter for the slight stall converter you have. This converter will allow the engine to reach its torque peak quicker and will allow the engine to flash, meaning that the engine gets a run at the stall point of the converter. This will hit the tires harder and move the truck quicker. Your eighth-mile time of 8.05 converts to a respectable 12.65 quarter-mile. With the converter change and intake manifold swap you could see a 0.2 reduction in quarter-mile time.
This is a perfect truck for making little changes and gains over the years. With the rearend and suspension setup, you can throw a good deal of power to it with no concern of breakage. Very soon, you'll need some sticky street radials or little slicks. Have fun ... we see 11s in your future.
Q: You may have covered this subject before, but here it goes. I have a '77 Chevy 1/2-ton and a '73 Chevy 1/2-ton. I want to replace the cab on the '77 with the cab from the '73. Now, the California Highway Patrol officer I spoke with could not give me a good answer-well, I think it was in the gray. What year will the truck be if this is done? I was hoping to have a ride without smog controls. What's the deal? Can it be done? Thanks for the help.
A: Well, after asking several questions of people in the know, things are still very gray. In my opinion, the body is the main section of the vehicle, and the VIN tag is riveted to the cab/body of the truck. The frame, engine, and trans are all component parts that are attached to the main section (cab) of the vehicle. We believe the vehicle would be registered as the body/cab. As you stated above, you have both of these cabs. We assume you have a clear title and pink for the '73 cab? This would be the only holdup we see about the swap.