1973 225 valve adjustment help!please!

One reason why it's easier -- once you've got the feel for it -- to get a proper adjustment with the engine running is that you needn't worry about making absolutely certain the valve you're adjusting is on the heel of its cam lobe. There's a good deal of rotational arc during which there will be some clearance between the rocker and the valve stem; if you adjust the clearance at the wrong point in rotation, your adjustment won't be correct. Also, by doing it with the engine running you can watch and listen to the effect of each adjustment you make (idle grows rough when you go too tight, valve begins to click when you go too loose) in real time. But here again, there is a bit of a learning curve to get a sense for what you're watching and listening to and feeling for. Since you're new and learning, you may want to use your feeler gauges to double-check and see how your static adjustment measures up with the engine running at an extra-slow idle as outlined at the previously-provided valve adjustment procedure link. Don't be afraid; you would have to do something really, almost deliberately boneheaded to get injured or cause damage.