In actual fact the Ford alloy crossflow head did get eaten out by some coolants, you had to use a specific coolant for it, ask cylinder head repairers. Seems it use to happen to quite a few motocross bikes as well, seems they had a high magnesium content in there alloys so you had to use coolant recommended for their particular use. Some coolants have descaling ingredients in them silica (abrasives), typically green coolant has 25% solids (silica) and red coolant has 15%. Japanese makes tend to use phosphates not silica in their coolant.