I dont have pics handy, but do have one suggestion- especially for the carts that have scupper posts only.. Add a pvc 4-way cross piece, slide it down over the scupper posts on the cart. Add pvc wrapped with foam coming out either way off the cross piece to create support for the kayak to rest on.. similar to the cart in this pic:
http://www.allkayakfishing.com/rigged/cart2.jpg
This way, the scupper posts will keep the cart in place, and aligned, but will not be supporting the full weight of the kayak. Will try to post exact pics later..