The 235 and the 261 had different cams. I can't find the specs, but attached a cut and paste from the 1960 shop manual showing that the two engines and different valve lash specs.
Matt
In late 1955 (Task Force) trucks the 235 cam bearings were changed to match the 261 cam bearings. I bet the "261" cam was used in all 235/261 engines sometime in 1956, as ApacheFiend" suggested.
The 1957 Chevrolet Truck Shop Manual explicitly states that the same cam is used in the 235 & 261.
Different intake&exhaust valve lash settings were used on 235 and 261 engines that used the same cam.
