I made one this winter but its down at the boat.
Was pretty simple. A couple of scrape 1x2 pieces of oak about 4-5 inches long. Drill a hole through the 3/4 face of each about in the middle. Cut arcs in one face of each to match the diameter of the engine's pulley. Put a piece of 3/8 all thread with nuts and washers through the holes in between the pieces. (all thread needs to be approx the correct length between pulleys) Screw nuts away from middle to spread the pieces of wood. Works well. No prying on delicate engine parts. Tight or loose as you want without having 3 hands. Part sizes may need to be adjusted as per engine.