The usual hard part of an impeller change is getting at the tiny brass screws that hold the cover on.
A slot screw driver is a PIA as it must be lined up well.
By removing the slotted screws and using Allen head SS screws no looking is required , it can be done by feel.
Best of all the Allen head screws will frequently stay on the wrench when reinstalling.
Purchase a box of 100 , as sometimes they don't , and fall off.
Remember the brass screws are weak , and so are the SS replacements , go EZ installing.
If you have a walk around engine room and can stand and address the engine properly , it still speeds up the process.