It's well worth the effort to toss the screws that came with the mount and get some quality socket head self-tapping screws from somewhere like microfasteners.com (where I get mine). I've dont nylon mounts both ways, drilling a pilot hole then running in a self-tapping screw, and by drilling a hole all the way though and using machine screws and nylon lock nuts. I actually prefer the machine screws, I can get the engine on and off a lot faster than with self-tappers.

How? Ah, there's the trick. I run the machine screws UP from under the engine. So the nut sits on the engine, and the screw head is easy to get to from under the mount. I don't even have to take the muffler off the engine to dismount it. I also like to use hex head screws and a ball driver to turn them. I chuck the ball driver in to my cordless drill. Now, just grab the nut with a wrench (or even pliers in a pinch) and spin out the screws. Using this kind of thing, I've preformed field engine changes between combat rounds in around 15min. Not quite a NASCAR quality pit stop, but not bad either.