I know this is an old thread. But just as a suggestion to others who may be interested. I am in the process of building a launch cart. Using an old (real old) Ajay golf bag pull cart, I found. Nice big wheels. Rusty, but it folds up and down. Nice long and extendable handle, that is adjustable up and down.
A little oil on pivot points, some sanding, and paint and she'll be beautiful.
The plan is to build the boat mount so the boat rides across the axis (parallel to the axle) of the cart. Rather than up and down... parallel to the downtube.. That should allow for easier conversion to a boat and easier to launch as well. And the shrouds/spreaders don't interfere with anything.
All the bag brackets are bolt ons. So moving them in position to use them for supporting the boat should be easy. A swimming pool noodle covers the downtube to cushion hull, from abrasion.
Proof of concept is complete. See early photos. Took about an hour. It works. And actually works very well, too. Will try to fit the bag cradles so they will support the front of the hull.
Another benefit is the cart folds up nice to ride in the bag caddie of my golf cart. Makes it SUPER for transport to the pond at our RV park. And once you get it there, simply unfold it, roll it to the pond, and unclip a bungee for launch.
Last item is to mount a water proof plastic bin on the handle to hold the radio. And some extra tools/batteries.
Can't beat the price.
http://s284.photobucket.com/user/burnsrm/media/IMG_0013_2_zpsh3t7pivo.jpg.html