[rotorwrench]

Welding and soldering are two different procedures. If a part is cleaned properly and a good flux is used, silver or brass will stick but old engine parts made of cast iron are very porous and hard to clean. The water jacket spaces around the exhaust pockets were one of the things that Ford engineers (Harold Hicks) and pattern makers had to improve upon in the initial development of the model A engine. The model B engine castings may have been even more thin in this area.

I've brazed up cast iron cylinders and heads for the early Harley Davidson motorcycle engines and never had problems but they are air cooled. When coolant or ethylene glycol has saturated the iron castings, it's almost as bad as oil to get it clean. An engine block would have to be cleaned very well inside and out to get a solder to fill into the porous substrate properly.

The ideal way to repair it would be fusion welding with cast iron but it wouldn't be cheap. Inside the exhaust pocket, it wouldn't be easy either.