Replace Thetford with Thetford or Valterra?

Recently acquired a 1974 Argosy 24 and doing a full rennovation. Need to replace both dump valves. If it's recommended that I replace the old Thetford valves with new ones, how do I determine which Thetford valves I need? Or can I replace the old Thetford valves with Valterra valves? If so, which valve(s) will work? I appreciate any advice. Thanks!