Hope it works out. I don't have any pictures, but I helped a friend lift a MacGregor 21 off its trailer using heavy-duty ratchet straps and a sturdy oak tree branch. We only raised it high enough to repaint the bottom, using a roller on an extension pole. No way was I crawling underneath that boat.
Whatever method you choose, an easy way to get started is to lower the trailer tongue as far as possible and place a solid brace under the transom. I've even used a picnic table for the transom brace (see picture). Then use the trailer jack to raise the tongue as high as it will go. This lifts the boat off the bunks so it's supported by the transom brace and the bow stop. At that point, you can slide straps underneath and begin lifting.
If you use straps to lift the boat, make sure they cannot slide forward or aft. Tie the lifting straps together fore and aft to keep them from slipping off the hull under load.
You'll also need at least one additional ratchet strap at each lifting point. Use the spare strap to hold the load while you release and reset the primary strap after the spool gets too full of strap to continue. Repeat the process until the boat reaches the height you need, then support it with sturdy homemade jack stands.
A stack of old automobile tires actually works very well as a support stand. I have some pictures of that setup somewhere if you'd like to see them.