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.
