Monitor Repair Help Needed

I am in the process of swapping the display unit from my model 5322 IBM System 23 with the display unit from an IBM model 5324 monitor (this is the monitor that went with the second, non-all-in-one version of the System 23). But, I've run into a problem. I had no problem removing the display unit from the 5324. However, on the 5322 I can't budge the two mounting screws that attach the monitor to the chassis of the computer. They are threaded flat head slot driver screws that go through flat rectangular brass washers and then into threaded sheet metal. There is no corrosion that I can see. What I've tried so far is liquid wrench with the usual tapping. Still can't budge them and have done some damage to the screw head tops, although they are not yet rounded off. I have read through various techniques on web sites about removing stuck screws, but many of these (involving impact drivers, etc.) seem too severe for working on electronics. Also, as one might expect, the screws are not particularly accessible. One I can reach fairly easily (and could conceivably be drilled out) but the other I can't and requires a long driver (10") just to get to the screw. If I could get the more accessible screw out, then I would be able to pivot the display unit somewhat which would likely help break loose the other screw. Any ideas?