So I have given the head gaskets much thought. Initially I was going to use 560 head gaskets and port them to correct a few mismatches in the cooling passages. The bore centers and locating dowels were spot on. But then they are thinner and designed for head/block of the same material. So I'm thinking about having the 4.5 gaskets modified for the larger bore but I can't find anyone that can do it. Custom head gaskets are $$$ for 1 set. They would need the bores enlarged and fire rings.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT