I need to replace the lever(over flow plate)
http://www.hometips.com/content/popups_intro.html

that allows the tub to drain,its wore out.

I bought the replacement at a big box store, there are two screws that hold
the overflow plate to the tub but I am afraid that I will twist them off
removing them, and don't want to have to replace the whole drain mechanism.
The old screws are tight, I need a big screwdriver with vice grips attached
to the screwdriver for leverage.

Any ideas?

thanks
Tom