How bad do you want to get those screws out...?
I say this tongue in cheek, but if you don't give a crap about the stock or screws, grab a pair of vice grips and have at it!
This was how I disassembled my rifle, but then again, I was sporterizing, so I didn't really care too much about what happened to the items I was taking off.
If you have a cheap screwdriver and a grinder, you could fashion a spanner for those screws. This deal would work fine on any screws which aren't in there really tight. If they are stuck in there though, you'll have problems.
You could try wrapping some tape around the screw to try not to mar the surface if you do opt for the pliers, you'll just have to give it a shot.
Let us know how you fare.
Unkel Gilbey