Today I had the time to clean the exterior of the engine, tape it off and spray it with the primer. It makes quite a difference.
What I had not yet mentioned was that I found a New Old Stock cylinder head to replace the cracked one. Amazingly I found it here in the Netherlands at just a two hour drive. It weighs about 700 grams (a pound and a half) more than the old one. I presume this is what has rusted away in 60 years. Anyway, I sprayed it as well.
I also replaced the studs from the exhaust manifold to exhaust flange (The thread had gone) brushed and painted it with a heat resistant steel color paint. Let’s see how long that stays.