A simple one for tonight – Spencer Heads.
Spencer Heads Inc., devised a way in the 1960’s to “recondition” Cleveland and Detroit cylinder heads (Unknown if they did anything else). I learned about these last year from one of Great Lakes Towing’s port engineers. The Spencer Head, took a standard 278A/71 cylinder head and machined out the bottom of it, and inserted a new base and valve seat assembly. The idea behind this was the help with heads cracking from around the valve seat – a common issue apparently with 278As when they are run hard for long periods or go through hard heat/cooling cycles.
It does not seem like this style of head caught on all that much. From what I gather, the original style heads are preferred over these.