Short Shaft Fan Clutch
That's the one I use. It works great! I can't fit a 18 inch fan in my '67 shroud so I had to go with a 17".
If you can fit an 18" fan Hayden 3618 or Derale 17118 will work. Looks like the flexalite 5718 has a steel hub and aluminum blades. Not sure I'd be comfortable with that one. Flexalite 5717 is their 17" version. Hayden doesn't have a 17" fan for that clutch. There are a slough of 19" fan as well.