One thing that has helped me over the years are ACR Phillips screwdriveer bits. They have anti-slip ribs on the blades. Here's a link that explains them:
http://www.aaronsscrewdrivers.com/anti-camout_ribs.htm
Here's a better pic of them:
http://www.asia.ru/upload_images/98/97356/1432456.jpg
One of these bits along with an impact tool will remove the cam thrust plate screws.
Impact tool:
http://www.vehicle-wiring-products.e...photo/5542.jpg
Now, after all that, I admit to just using vicegrips to loosen (and tighten) those screws. I detest doing it, but it worked well. Left a few gouges. Next time, I'll use the ACR bits I forgot I had.