The selection of old projects sounds exciting! Indeed, the spring lengths of Stith rings varied according to the size and spacing of the scope tubes; it is usual practice to shorten or fabricate a new one. The plunger type allows faster detachment with a little more movement over time, while the rail type provides good repeatability but slower removal for B&L/Kuharsky setups. Once you have the 722 or Mauser constructions mounted, I would really like to see pictures!