Hi wonder if anyone can help. I am restoring two big healeys, one a bj8 and the other is a 1957 100/6 that is being restored as a 1959 3000 works replica. My query is cylinder heads, my bj8 has a AEC 960 head and the replica has an engine I am rebuilding from bits I have acquired and the cylinder head is AEC 721. Both the heads are 12 port and when they are laid side by side they are exactly same in casing, holes, etc. I am about to send the AEC 721 for cleaning, skimming and new larger DW valves and guide and new harder seat. Does anyone know what is the difference is between the two heads if anything.