Look up FHA and NAFA both fur houses have excellent online fur handling manuals. Although I don't think they have the plans for an adjustable stretcher, they have the dimensions for a solid coyote board. From that you will be able to figure out your adjustable stretcher. The tips of my stretchers either have a leather strip tacked along the top edge, or a headless nail holding the two halves together were they meet at the snout of the stretcher. Both methods allow movement while holding the halves together.
I have never stretched a coyote on a solid board. But, I have come to prefer a solid board for cats. One tip: After the cat is stretched on the board I insert the belly board from the mouth end of the pelt instead of the belly end. I think I would do the same with a coyote on a solid board.
