Nofords another option is a manual impact screwdriver. A mechanic buddy turned me onto these when I was in rust removal mode. They are under $20 and can be purchased at sears etc. they basically work by hitting with hammer which turns screw. If possible apply a little heat then use impact screwdriver. Good luck as rust worms do not give up easily.

Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
Things may come to those who wait...but only the things left by those who hustle."-Abraham Lincoln