A 100 hp Pattin was just removed about a mile from Cairo WV last month. The new owner said he has some of the original wooden patterns for the engine. I think it is # 3. The one Earnie has I'm sure came from McFarland WV thru Tom Schoolcraft. The pumpers always removed parts off it to keep Cairo station up and running. What are you missing ?
If you're not intimidated by making parts to get it to run, who not make a valve? I would think a plug valve would be fairly easy to machine. most ball valves have some kind of a plastic seat, which would make it unsuitable for exhaust.
Good luck with your project that should make a nice rare engine. Has anyone gone to look for the original compressor(s?) for that engine-it was mentioned in another thread?, be great if they could stay with the engine even if not on it!.