So here's the best I can tell you. I've got a picture of our boat sitting on the dirt a few weeks ago. You really can't tell much from the photo, but if you sat the bike down on level ground by itself, the boat would sit seriously bow down. That's due to the keel down under the prop. A few months ago I had the boat out of the water sitting on a grid and it shocked the hell out of me. It was bow down enough that it made me nervous working on it. I think I have a picture somewhere and I'll look for it. So to answer your question best I can, i agree you will need to support the keel back a bit aft of the rear of the cabin. The keel drops down in that are and I would think you'd want it sitting on a solid surface back where it has dropped down. Then I'd want to suppport it closer to the front, say where the first stanchion is in front of the cabin. But that support will need to be something like a foot or so taller to level out the boat. It would be nice to get one more support under the keel, maybe between the two.
i suppose you could do away with the two front ones and just have the boat sitting down solid at the back, then on adjustable stands, similar to what you see in the picture.
It will certainly be a bit of a puzzle, but really shouldn't be that bad.
have fun and good luck