1971 slant six 225 no spark or weak spark at plugs?

you could attempt to repair the brass radiator with solder: drain and invert the rad. use a stainless wire brush and clean the joints, apply flux and heat slowly until the flux starts to boil and smoke, then add silver solder and allow it to flow into the leaking joint. Pull the flame away and allow it to cool. It should fill the cracks. Here is an extreme example of applying LOADS of flux and then the solder. Flux cleans and shields the base metal from oxidation. Solder and old rad solder has lead in it so please do this in a well ventilated area preferably standing upwind of the draft. Once the solder has cooled, rinse old flux off work.