Can I use this recipe for a one rib prime roast... the recipe says 2 to 4.

Yes, it works just fine.

You definitely need a probe thermometer. I made a one rib roast for Christmas Eve. Also important to take it out and let it rest before it gets to internal temp that you want.
Cheers
irina

I'll repost my answer here, just in case you didn't see it on the recipe thread: You could try it, reducing the cook time proportionally (see the chart above), but I'd strongly recommend a probe thermometer to keep track of the temperature (they're cheap!).