Nice 94 Carbine. If you are uncertain on how to remove that old finish, it might be better to find someone who refinishes old furniture and have them remove the old stuff. You could strip it down first so that only the stock is taken to the refinisher. Then either have him refinish it with BLO or you can do it yourself.
You might try a bit of penetrating oil on the rear screw. Take a screwdriver that fits the rear screw well, and put it in the rear screw slot. Then give it a good tap with a hammer, to loosen the threads of any crap in them. Next, take some penetrating oil, and dipping a q-tip in it, apply the oil SPARINGLY on the end of the screw that you can see from the top at the tang. Leave it for about 12 hours and repeat the penetrating oil on the screw end. Do this a couple of times.
You can buy hex screwdriver bits about 4 inches long. Use a socket that will fit the hex bit, (about a 5/16 socket) and a ratchet wrench handle on it. Have someone hold the rifle upside down on a table, and you can use the well fitting screwdriver bit and socket/ratchet handle to turn the screw slightly. The reason for the ratchet wrench is that you might have to move the screw back and forth a bit each time to loosen it up, and each time you will be able to turn it a bit more, and finally get it out.
I would advise you to have someone holding the rifle rather than clamping it down, which could put a dent in the wood. While you could use a bent screw driver to remove the screw, it is better to use the above method as you have more control and can use two hands on the socket wrench, putting a bit of downward pressure on the bit to keep it in place.
An alternative method of removing really tough screws is to clamp the piece in a drill press vise, and put the hex bit in the drill press. you can use downward pressure to keep the bit onto the screw and turn the drill press spindle by hand by pulling on the drive belt. Again two people are best, and unplug the drill press first. In both cases, you might have to file the screwdriver hex bit so that it fits the screw head well.
Most American screwdrivers are the "keystone" type where they are tapered inwards at the bottom. European screws tend to have parallel sides in the screw slot, so the American keystone screwdrivers contact only the top of the screw and has a bit of a gap at the bottom, thus tending to slip out of a screw head more.
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