The Snap On extension that eases this job greatly is FLXM13. It costs $50, but will save lots of trouble. The shaft is only 1/4" so it will feel like you are going to twist the shaft in two, but just keep torquing on it.

Since the job is so labor intensive, you DEFINITELY want to use a quality pump. Also buy the short piece of hose at the top of the pump and the thermostat, then cut away the old one to ease getting the pump out.

Good luck,