Harry Greb would have fought Spinks jinx and the chances are that he would have beaten him at some point in a series of three. This is the kind of challenge you have to be up for if you want to be the greatest 160 lb fighter of all time.
Marvin was a perfect 160lber, Spinks was an excellent fighter at 175lbs...years ago 175 was a haven for middleweights and a lot of them moved up to be succesfull, however Mike was a true 175lber and a strong one at that. I have him in my top 5...Spinks could wack but Marvin was solid, I see Spinks winning a close UD in a fight he controlled but Marvin tested the water...just that Spinks had better wiskers than Hearns until he froze vs Mike but Mike scared a lot Bigger men than he.
A great big man will always beat a great little man. Hagler carrying an extra 15 pounds would have been too much to ask.
Greb probably would have weighed well over 160 pounds for Spinks. Greb typically weighed 165 or 166 pounds, often more like 170. He was a light-heavyweight really.
Hagler wasn't even a big middleweight, like Monzon or Briscoe were. Hagler had quite a small skeletal frame with some impressive muscles. See him against Leonard, Ray is just as big as him. Spinks would have probably outpointed Hagler, who wouldn't have been effective weighing anything more than 163 or so.