Adding into this thread for a similar problem with a 1960 vintage 261. Initially cylinders 5 & 6 intake values were stuck (hadn't been run by previous owner for years). Pulled the head, redid the values and guides. After reassembly I set all gaps cold and everything looked fine.
Having started the engine and allowed to get to operating temperature in order to do the final valve adjustment, I noticed some odd "mild clanking" (best I can describe the sound. Pulled the valve cover and cylinders 5 & 6, both intake and exhaust have rather large gaps, even after running the adjustment screws out almost all the way (see picture). Cylinders 1-4 seem OK. I've checked the rocker arms to cracks, etc... look good. Unless the machine shop actually did nothing and charged me anyway.... seems unlikely to be stuck valves still and they seem to be similar height to the other valves (will measure precisely later today).
Question is... any other thoughts of what might be going on. Before buttoning up the side plate I double checked that all the rods were properly seated when doing the cold gap adjustment. The only other thing I can think of is the camshaft lobes are worn down... but that seems a stretch.
Ideas and suggestions welcome... Thanks guys and gals
