What kind of exhaust manifold/header are you running. I had a noise in my 270 GMC I thought was vale train related. I readjusted everything. I changed the lifters, push rods, rockers and rocker shaft. I checked the valves and valve springs. I could not quiet the noise but I knew the valve train was OK. Years went by and I changed to cast headers from tube headers and the noise went away. Just a thought. Beater
