The 900 kg proof pressure would likely cause confusion if someone tried to convert to psi. With the proof dating from 1974, it would be a crusher vs transducer measurement. Like LUP vs psi.

Re a Spanish double meant to compete with the Model 21: That doesn't ring any bells. However, Winchester briefly imported (mid-70's) a sxs they designated the Model 22. Made by Laurona. Not often seen.