Im building a Craigslist find 1976 z50 for my son and will have-lots of questions so here is the first. I removed the head and the valves and they have a slot cut in the cylinder facing surface. The intake looks ok, the exhaust after cleaning seems-to be filled with something that looks like weld spatter. On the cam end it looks like the center of the stem is a different material. None of the replacements, aftermarket or oem, look to be made like this. Any thoughts?