set of x heads for sale

Look at the exhaust valve spring retainers. Notice how they look differant from the intake retainers. If you were to remove one, you would find it is sorta like two retaners with a bearing in between the two. Its purpose it to allow the exhaust valve to rotate as it opens and closes. The are mostly used in HD aplications, like trucks, but never high performance use. Your factory 340 springs would also have had a damper in them, it looks like these do not. Most likely when they were rebuilt, someone swaped these parts, but it doesnt really matter, if someone rebuilds them again, they will likely replace this stuff anyway.