The bone yards here were full of 2.7 powered cars that trashed motors until scrap went sky high.I had a guy give me a car with a bad motor. I called around to find a used motor and was laughed at 100% of the time. I sold some body parts off of it and scrapped the rest.
It takes about 6 hrs to do one if you have done them. I strongly recommend you install the updated timing chain kit and replace the tensioner. Valve covers,upper intake and timing cover have to come off to replace.
Sorry, was just having fun. I'm not sure what all is involved with a water pump swap on the 2.7. I never got that far with mine. I hope someone chimes in to help with your problem and I'm sure they will.
The biggest weaknesses of the 2.7's were the water pump and timing chains. Since the water pump is driven by one of the timing chains, I'd change the timing chains while it's apart that far.
It seems like the flat rate manual calls for 8-10 hours to change the timing chains.