**Note: In order to use these camshafts in 1955-57 265ci blocks, it is necessary to machine a small groove in the rear main journal of the cam to allow oil flow to the top of the engine.

***Note: Beginning in 1987, most of the V-6 and V-8 engines were equipped with hydraulic roller camshafts. There are differences in the block to accommodate a cam retention thrust plate and the anti-rotation mechanism for the lifters. These blocks are identifiable by bolt holes for a cam retention plate under the upper timing sprocket, as well as bosses and tapped holes in the lifter valley for lifter retention hardware. The camshafts on these engines have a step nose and smaller bolt circle on the front of the cam. An earlier model camshaft may be used in these blocks by using the appropriate timing chain set and adding a thrust button when using a roller cam.
1988-99 Chevrolet 305 and 350 V-8 engines (and some 1987 350 V-8 engines) use a different configuration camshaft core than the 1955-87 engines and cannot be interchanged.