You don't need a timing gun to do this. I just replaced one on a D16Y8, and it took me about 4 hrs (was my first time). As long as you follow those instructions properly it's not that hard. The 3 teeth rule is to take out the slack on the other side of the belt, and when you tighten the tensioner with this slack out it'll give you the proper tension. Just remember to triple check your timing marks before starting the car. Make sure the cam gear, and crank pulley line up on their marks, and make sure the rotor button is pointing at the #1 spark plug terminal on the the distributor cap. Then manually rotate the crank pulley 3 or more revolutions cc, and check all the marks again. You do this to 1 make sure the pistons aren't going to hit the valves, and 2 to make sure your marks still line up. All in all the hardest part was getting the crank pulley bolt off. 150PSI impact couldn't get the job done. I had to get the crank pulley tool from drivewerks.com, use a 2 ft breaker bar and push with both legs while leaning back against a wall to get it loose (it'll be much easier next time around).