I too am assuming you have the head off and it would be a simple matter of pressing in a new one. However, make sure you get the protrusion correct. I have only GMC books, but I'm sure the Chev books gives numbers too. If you do install one yourself, you need to have a small hole gauge and a mike to measure the clearance. It is quite common for the new guides to be too small in the bore and the valves seize once the engine gets hot. Reaming new guides after they have been installed is quite common.