Spinks, Archie and Ezzard. I don't think any other LHW's would beat Ruiz TBH. That includes Conn and Tunney, I really truly don't think they beat him.
I think another guy who gets minimal credit for successfully moving up in weight decisions Ruiz--Adamek.
Charles Moore Spinks Tunney Conn Langford probably as well. Does Michael Moorer count? If Spinks does, MM should as well given how MM started at light heavy.