Everything coming off the assembly line today has positive style seals on it....not necessarily Teflon but positive style seals. You also didn't mention what heads/guides/application. Iron, aluminum or ??
Just standard BB iron heads, 915, 906, 346 or 452, I think they're all pretty much alike save for the closed chambers of the 915's? I have access to any of them. My '69 (~ 60,000 miles) has never been apart, I'm sure the original nylon timing gear is beyond brittle and the valve stem seals in little pieces all over the engine.
