I have tried two aftermarket latches without being satisfied. I ended up replacing the spring in the old ones after soaking them and cleaning them in varsol (actually, it was spray gun cleaner). Work like a champ.

1951 1/2 ton 3 window
1949 Suburban
http://gallery.mac.com/patrick.plummer#100287&bgcolor=black&view=grid
http://gallery.mac.com/patrick.plummer#100501&bgcolor=black&view=grid