Non of the aluminum block heads have any benefit for my project over 4.5 K-jet heads. I went out to the garage and measured some parts. The 5.6 intake valve is 46mm vs 44mm for the 4.5. The 5.6 combustion chamber is 98mm wide at the fire ring vs 94mm for the 4.5. the 5.6 valves are 90mm wide in the head so technically they would clear the cylinder but the 5.6 combustion chamber is wider. If you used a 4.5 head gasket it would not seal so you would need a 5.6 gasket which would leave a lot of space between the fire ring and combustion chamber. So IMO the 5.6 head wouldn't work with a 92mm bore. For me not worth the lost CR for a tiny bit more intake valve.

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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