Get out some soapy water. Assuming the bottom of the pump housing and liner are in place, lower unit on the work bench in a vise with drive shaft up.
Install the impeller locking key in the slot in the drive shaft. Some Vaseline petroleum jelly will help to hold it in place while you do the next step.
Get the impeller good and soapy then slide down the shaft and into position, ensuring that it slides over and locks into the slot in the impeller key you just installed.
Slide the cover down till it touches the impeller blades.
With a pair of Vise Grips, rotate the DRIVE shaft CW as you look at it at eyeball level still in the vise and while doing so, start putting pressure on the cover assembly. As you continue the process the top outer tips of the impeller will fold back and slide under the cover and continuing, the whole impeller will be consumed.....keep pressure on the cover after that happens and you locate the mounting bolts and get them in place.
You need some sort of seal at both ends of the copper tube and it has to be relatively straight.....on newer engines, (my 2002 had it) there is now a bracket in the midsection that holds the tube in place while you remove the LU making it a LOT easier to get the job done.....no looking up into the bottom of the block, trying to stab the tube and hold onto it while you manuever the LU in place.
Some have posted that the impeller will correct itself. I have never seen a cutaway of one in action and doubt that many if any person has seen such, other than OEM test engrs/techs. Common sense leads me to believe that the blades do not have enough space to do that considering the last ⅓ is all that beds as proven by the shape of old impellers that have been sitting a long time and have taken a "set".....permanent bending of the last ⅓ from sitting for long periods in the cramped part of the eccentric water chamber.
You don't need new parts. The resiliency of the new one you just installed will allow you to pull the cover up, spray with soapy water, and twist and push as I stated above. The impeller doesn't get brittle for a very long time.....I took the one out of my '02, first time changed, in '12 (10 years) and although it had a set, I could bend the blades back to straight and there was no cracking of the back side where it had been crimped, kinked line showing, but no splitting of the material. It inched back to the set condition, but the point I am making here is that it wasn't brittle.
