The J-36 was the third design that J-boats produced after the J-24 and J-30. It was a fractionally rigged design that was not rule based but which was set up like the ocean racers of that day in terms of interior layout and deck plan. They are very good boats for that era but are a bit spartan down below.
J-boat eventially cut down the hull mold for the J-30 and used the weight savings to add a heavier, more efficient keel and an optional masthead rig to produce the J-29. That treatment was so successful that J-boats cut down the hull mold for the J-36 and went to a simplified deck plan, a deeper/ heavier keel, tiller steering and a masthead rig version that became the J-35. The J-35 is a very versitile design offer good performance in a wide range of conditions. Later J-35''s were offered with an optional pretty full interior but of course minimal headroom and cruising gear.
J-35''s are still competitive race boats typically rating somewhere around 72 and still with active one design fleets in much of the country. The J-35 is generally considered 9 to 12 seconds a mile slower, especially in a lighter air venue like Long Island Sound. The J-36 is actually an easier boat to handle and certainly the easier of the two to single-hand assuming that the deck layout has been modified.
Three reasonable alternatives to these boats would be the Express 37, Frers 36 (F3) and the Farr 11.6, each with their own advantages and disadvantages.
Great stuff Jeff. To the OP, if you're going to do some racing, it's all about a boat's ability to sail near it's rating and the cost involved to make it do so. As Jeff mentions, and it can never be repeated enough, before you buy any boat, talk to several people to get an idea of the actual cost of running the boat that's caught your eye. A quick call and a couple of ball park estimates from a sailmaker is one of the first things that will reduce your dreams by about 5' LOA (if not more) in a heartbeat!