The 31's are getting old. You can spend a lot of $ and sailing time fixing them up. We looked at a couple when buying our current boat. They were drastically different - kits - so I do not know what your boat may be like. That is the biggest wild card - who did the work.
But, they do have a classic look and long overhangs. This also means a short waterline - slower unless tipped. Also your accomodations will be smaller than in a 31 without the long overhangs. But if you get her tipped over she should speed up nicely. I like sailing at < 15 degrees on my boat's
lines and going fast.
You could really umph up the interior if you are so inclined.
Due to different owners finishing them, the engines could be anything. I think we looked at ones with atomic 4's.
I hope this helps.