If you know for a fact that your water pump is leaking, you otta change it as soon as possible so you don't have to get towed home.

 

Just my $.02 worth.

 

Just changed mine on a 79. You do have to remove the A/C compressor bracket to get it off (real pain in the ***, as it has bolts in the exhaust manifold in addtion to a couple into the head and then a support bar down below.  DON'T unhook your A/C hoses...just lift the compressor out of the way a bit - the reason you do this is it shares mounting bolts with the water pump. My solution - good bye A/C, wasn't working anyways and I don't drive the car with the roof on.

 

The "heater only" pump you got is correct. That refers to the side port on the pump. It comes with a plug sealed into the top and a threaded port on the side for your heater hose.  Before you do anything else, remove that hose fitting with a 7/8 inch wrench prior to pulling the pump off the block.  It is in there tight (if like mine). I cheated and used an impact wrench - came right out.

 

have fun and good luck. Seal it up good with RTV or Permatex #2 when you put the new one in.

 Be carefull! I started out with a bad thermostat, and it turned it into a complete body off restoration project.

Check the wp shaft lenght, I bought an aftermarket CSI shortie pump and I had to do a little shim on the wp shaft to get the pulleys to line up. Not a big deal just annoying since the vette shop recommended it as a replacement, it's not worth the gas money or time to go exchange it. I went with SS bolts on the thermostat housing the old ones were rusted tighter than a ducks behind. One refused to come out no matter what I did, torch, pb blaster soak and finally drill and extract and I still ended up fudging up the threads on the intake anyways.