First things first, Bob-- get good measurements. I measured where the poppets (swivel platforms) met the hull when the boat was on stands
I drew up a very nice 6-legged cradle about 5 ft wide and about 68" high. The vertical legs meet the boat where the bunk bulkheads are inside; the front space is 75" and the rear space is 69". Don't plan for them to be anywhere else. A keelboat should never sit entirely on the keel-- that leads to damage. It should be at least equally supported by the poppets that meet important structural points on the hull.
As for the poppets themselves, buy them from any dockyard/marine supplier. They're about $60 each or so. Make the legs only as tall as the shortest one needs to be, leaving room for the screw of the poppet assembly to make adjustments. Mine is drawn to use 2" pipe for the verticals. Rebar is adequate for corner braces so long as it is in straight lines when welded in place. The u-channels are like 2x6" or 2x8", standing on edge. There are 2 crossmembers for the keel shelf. And the 8" u-channel into which to set the keel bottom should be mechanically supported at both ends (should be strong in place before it's welded).
Though 4 legs is adequate for the weight and shape of the boat, 6 legs is preferable because you can easily lower one to paint the bottom without worrying the boat will fall over.
I haven't had it built yet, mainly because I am not sure where the boat will be hauled-out next. But I have the plans if you can adapt them to the 260/270 (a boat I don't know enough about).
If you want to engage me I will locate one of these boats and design you a decent cradle. Be prepared-- I tend to prefer overkill!
Do let me know how you do on this. E-mail me any time.
