I saw in the specs section my engine should have 170 - 225 psi compression. When I do a compression test, when should I begin to be concerned about the results? In other words below what psi should I think about a rebuild? thanks

depends on your taste, hehehehe. My old truck peaked at 117 with a recommended min of 160. Ran like a dream.
Other then that, ignore my babble.

Your biggest concern should be with how much each cylinder varies from one another. Compression below 170 means that the rings/and or cylinders/or valves are getting worn. The engine may run fine, but if your compression is in the 150's, then you will probably be consuming some oil between oil changes. Now, as for cylinder pressure varience, you want NO MORE than about 15% pressure difference between cylinders. So lets say you have 175 psi on 3 cylinders, and one the one cylinder you have 140 psi, that isnt good. You basically want your highest psi cylinder, to be no more than 15% of the lowest psi cylinder. Cylinder pressure that varies several to 10 psi from cylinder to cylinder is just fine. If all your cylinders are at 170 and above, all within 15% of eachother, then I'd say your motor is in pretty good shape.