100% with you on that jasperrc, I will not for one second trust just the 2 pivit screws to hold the engine in place. It is very important that your engine mount can be lock down tight. I will say that you are on to something with the adjustable engine stand, throw in a 1/4 scale servo, a couple of cams, and a 3rd channel radio, then you would have a boat that would have a good take off, top end and one that would be hard to get stuck.
I'm not sure on your plans of connecting the stand to the hull, I recommend haveing as much as possible of the engine stand legs tied into the hull. On all of my boats the engine stand is connected from the transom all of the way to the grass rake. Just keep in mind that the engines may be small, but once they are loose, they are some mean sons a guns.