Radar's (Francis) GMC project got me interested in the Gonkulator database for the old GMC. I dont have one myself and data, stock specs, is really sparse. Can anybody provide any of the following:

* Stock rpm/tq and rpm/hp for the 256cid, 1year only

* Stock cam info - lift, duration, lobe centers. Duration at .050" is ideal but of course unless somebody measured it, that data just wasnt listed back then.

* Was the stock cam the same, 228 thru 302 or did the lift get higher, etc?

* Stock carb info for 228-302, CFM great but even venturi/throttle diameters would help.

Like most engine families I start out guessing at the stock specs and then fill in the blanks. Google not too helpful in this case!
Much Thanks

Hi Duce Coupe,
It's me again, Francis, (not the Pope), but I go by Frank Hainey.
I have a maintenance manual for 56 GMC Trucks that covers the 302 and 270 engine. You may be able to extrapolate the horsepower to the 256 engine. Here is what it says about some of the data you are looking for. The 270 figure is first followed by the 302. If there the same only one figure shows. Horsepower 34.35,38.4 (SAE-AMA). The 38.4 figure converts to something like 145 hp I believe in todays language. Valve Timing: Intake opens BUDC 14, Intake Closes ALDC 58, Exhaust opens BLDC 64deg 28 min, Exhaust Closes AUDC 32 deg 14 min. hope this helps.