On one of the cylinders I had (many years ago) managed to break the second cooling rib, the only way to repair it was to also cut off the rib above it.... In total there were 5 damaged ribs on the cylinders and 1 on a cylinder head. I took some aluminum plate and made all the missing pieces, Aad welded them in and I cleaned up the welds and then blasted the heads with coarse grit because the repaired areas were smoother than the cast ribs. The grit made all the surfaces look the same, after that i glass beaded both heads for a nice satin finish.