I had 3/8" in mine. I would suggest using a thread chaser to clean up the additional threads when you change to the 3/4". Mine were full of carbon and I was scared of stripping the threads in the head.
Hope this helps
NO!!!!
I've seen it. It never dries out.
Use a pressure washer with a sewer pipe cleaning jet that will pull itself through the frame-be very careful as these jets of water can cut/kill you. After it has dried out use an oil based rust treatment in a garden sprayer to soak the insides. Repeat...
These seats are in very good unrestored condition. One tiny tear that could be repaired easily. They are missing the canvas straps, which are available new. There are some minor surface rust stains. I've had these seats for 10 years sitting in my basement. I now have a baby and need a sammi seat...