Thank you very much for the information!
I was in contact with a shop specialized in rebuilding Ford v8 engines earlier today. I will probably send the engine to them to check if it has to be rebuild. They know the 351c-engine quite well and have a good reputation in Norway.
If the cylinder heads are in bad condition they recommended me to buy new fully assembled aluminium heads instead of rebuilding the old ones. I've read the CHI heads are great. Is there any big difference between the 2V-190cc C1/C2 assembly, 60cc or 67cc combustion chambers models? I'm focusing on low-end torque.
The engine is fitted with an Edelbrock 1806S Thunder carb.