Some GMC rocker arms will fit Chevrolet 216/235s. It's roughly every 4th one or some such. The only reason I know is that my 248 broke several rocker arms and I only had Chevy parts to play with so I went ahead and tried them. They fit fine, just a little different in shape/size.
Some of the rocker arms work, at least half don't due to the different valve angles.
Jeff
