I had a bimini made last year by JSI down in St. Pete. http://www.newjsi.com. They may have saved the measurements. It's mounted on the top of the stern rails, has an opening in the center for the backstay, and ends just aft of the boom. So, it basically just covers the area over the wheel and the aft portion of the cockpit.
The problem I had with trying to put up a bigger bimini was headroom. If you put it low enough for the boom to pass over it without hitting it, you're not able to stand upright at the wheel. I think tiller-steered boats are better suited for biminis as you usually steer sitting down, and a lower bimini isn't a problem. One potential solution is to have the clew of the sail recut a few inches higher so the boom will ride higher. Another problem I had with trying to fit a regular bimini was finding a place to mount it. I've got 2 sets of winches, so it's tough finding a spot where the winch handles aren't hitting either the frame or the straps. Lee Scott '87 C-27 #6350
