[vettestr]

Clois,
As an X drag boat shoe I also saw a lot of electrolysis. The fiberglass hull like our toys made for a grounding problems. The combination of many different metals bolted together (steel block = copper head gasket = alum head and so on....) even without electical components like fans still generates current flow.
Ground everything and run 2 quarts of anti-rust or water pump lube as sold by Prestone or many others. Using distilled water and 50 percent coolant is my mixture but any good mix. The distilled water lowers conductivity because minerals have been removed.
Why do you need a custom size Rad? Many good units are available for far less than 800 bucks but I know it is not hard to spend that and more for some name brands. I also have used several of the 250 dollar unuts with good results?