You should scribe the position of the steering valve prior to removal. That way you know where to place it when reassembling. Hope you also replaced the steering vane seals...that's huge!
The air is likely coming from a bad seal in the power steering pump. They have 4 seals. (Originally 2 double seals) 2 keep air out, and 2 to keep oil in with a shim in between.
It all relative. Those are 60 plus years old. If they are in good condition and you use the correct power steering fluid from John Deere, they work great. A hell of a lot better than manual steering especially if you had a mounted corn picker on one.
