Hi Nick,

Norm is right, a impact driver is the best choice as it applies downward force and torquing force at the same time. It is the best tool if you want to save and reuse the bed knife. A manual impact driver is struck with a hammer, for example: http://www.amazon.com/Ko-ken-Attack-Driver-Set-An112a/dp/B002P8ARLC

The problem you have now is that you can't get enough purchase on the slotted head screw because they are already stripped. You would have noticed that your screwdriver was cambering out.

What I did was get a dremel with a aluminium oxide grinding wheel/disk and cut the slots deeper and wider. Then I used a large flat head screwdriver that was as wide as the slot in the screw. After soaking the bolts in wd40 (both sides) and afterwards heating with a butane torch (for at least a couple of minutes), I was able to remove the screws. However, use a screwdriver to pry from between the blade and the sole plate to free the csk heads first, it will make things easier. My bed knife was already wrecked and too thin, so I wasn't thinking about saving it and if you use my method you will probably ruin the blade anyway.

Before I attempt any of this I re-attached the bed knife to the chassis and used a couple of trestles, some steel channel and clamps to ensure everything was secure and I could get above the screws to apply enough downward force.