Timing belts are simple to do, just some are s#!ts to get into, one trick I learnt early on is to use a small bulldog clip to hold them onto the cam shaft cog while you set it up on the rest of the cogs, always put all the slack to the tensioner side, and check your marks, roll the engine over check again and repeat, I usually check the marks no less than 4 times, I have had them walk before, but the best thing you can have is some patience, don't rush the job or you will run into trouble.