To close the loop on this one, I had purchased an NOS 1968+ version valve plate (19656) and installed the 1968+ matching head (2995) thinking that I was going to make out ok. It turns out that I overlooked the service valve seal style which changed from the 1960-1967 Rotolock (with teflon seal) to a Tube-O design (with O-Ring). So out came the compressor. I have a couple of heads, but the valve plates are questionable, so have a correct NOS one on the way. But I did save about $50 the first time around lol.