I would bet that a previous owner had a similar problem as you with the frozen bolt, and used a cutting torch to "remedy" the situation and figured one bolt would be good enough. If the metal is sound on the rest of the cross member, I would weld in a patch and drill a new hole. There appears to be plenty of leaked oil on your cross member to have kept it protected from rust.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission