Looking at that pic, if it was me i would wire bush the fins, rub down the smooth areas with soapy water and 1200 grit wet & dry paper, mask off all surounding bits with masking tape and news paper and spray the lot with sperex VHT engine silver in a spray can. It will need to heated up to cure, any over spray can be cleaned off with white spirit or Meths (no drinking it though).
Holding the can aprox 6/12 inches from the engine and useing short bursts of spray keeping the can moving at the same time.. IE: PPssst to the left PPPssst to the right not PPPPpppsssssstttttttt so it all runs all over the shop fills up the top of the can and runs all over your hands...
Makeing sure I shake the can for a good while else it will clog up and probly explode when I pierce it to get the rest out coz it cost me £6.50 and i'm damed if i am are going to waste it

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That is what i would do any way.