I know the 79 and 80 is pressed on. 77 should be as well I would think. you just need to borrow the tool kit from a local parts store. I used one from oreilleys.
it's pretty self explanatory once you get the kit in your hands, but there are also a few videos on youtube that show step by step.
you use the tool to pull off the pulley, and to press it on to the new pump.