I don't have specific plans. I've built a cradle once from wood, but it was for a 26' inboard powerboat.
It consisted of 8x8" rails running fore and aft for the base (sort of like sled runners), and there were 8x8" cross members spanning at bow, stern, and midships. Then 2x10s were mounted diagonally to support the V-hull, with vertical supports at their outboard ends to take the weight.
I realize that's not much help for a keelboat.
I think this is a practical alternative if you have access to timbers, or trees, and a guy with a portable bandsaw mill. Otherwise, the timbers might be prohibitively expensive. Hiring a local welder might be a better option in that case.
Sorry I'm not more helpful. Good luck.