Several years ago, I reworked a cylinder head for an Oliver 6 cylinder tractor. The intake valve stems were worn out, and the guides were all egg-shaped. Oliver parts were obsolete and unavailable. I substituted Chevy 6 cylinder intake valves and guides, which were a drop-in swap, the only difference was the diameter of the valve stems. I believe the Oliver stems were 3/8", and the Chevy was 11/32". The OD and length of the guides were exactly the same.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!