I use a 4 x 4 yard timber from Home Depot/Lowe's. I cut a 4 x 12 piece of 1/2 plywood to mount the engine (just cut a notch to fit the specific engine). I mount this plate to the 4 x 4 with deck screws and use bungee cords to mount the 4 x 4 to something that won't walk down the driveway. (I've even used the tail gate of my truck.) I then mount the tank and push rod like CharlieP above. I don't fuel proof anything. Just toss the ply plate and make a new one for the next engine test. You'll never need anything fancier unless you're doing this for a living. This has worked well for me for many years and never had any "close calls" with anything vibrating apart. By the way, I once used C-clamps, but they tended to vibrate loose due to the compression of the 4 x 4. Use lot's of bungee cords!!

Paul