If I could help a little here. You don't need any special tools or clamps, keep the job simple, remove the old impeller with a pair of angled long nose pliers. put a wet n dry vacuum hose up the pipe to suck out any old bits of impeller or debris. Before fitting the new impeller, grease the splined shaft with waterproof grease, put some washing
up liquid on your finger and coat the inside of the water
pump, lightly coat the impeller with washing
up liquid and slide it into place. Replace the cover. The vanes can will pop into proper position when you start the motor
. Job done !