Hey Segaboy. I gave you a big long post on SM.net on this subject.
I really think you are just fine here. However, if you absolutely MUST pull this cart apart, there were a few minor suggestions I made on SM.net.
Probably the best suggestion I offer is to try a new/different security bit. I've gone through quite a few of them myself...they seem to wear out as easily as the security screws strip....which is very easy. A brand new security bit might be able to grab that potentially stripped screw head just enough to tip the scales in your favor. I've met a whole bunch of different security screws that thought they had what it took to defeat me. I spit on most of their graves.....well not really most of them are in safely replaced in their carts and are being stored securely and with care. I was still the victor!
Let me know if you need any pictures or anything. On SM.net I focus a little more on trying to appease your worry and potentially getting the screws out...here I'll focus on trying to affirm that the board itself is legit.
Once you get the thing apart it will be VERY EASY to tell if its legit or not because official Nintendo games literally say NINTENDO on the circuit board with a copyright year and, of course, the chips.
Here is an example of some official boards:http://www.digitpress.com/forum/showthr ... ost1636822
As you can see, there are varying boards for different types of games (all EB boards will be identical but won't necessarily look like a Donkey Kong board) and the word NINTENDO is basically stamped everywhere it will fit.
If you are hard-pressed for peace of mind (and I certainly understand if you are!!!) than I'd be more than willing to take a few pictures of my EarthBound boards so you can compare. You'll have to get those screws out first, though.
I can also confirm that all three of my EB boards look identical to the first picture in the article linked by Mato. The bottom picture in that article probably is counterfeit, since I've never seen an EB board that looks like that and I've pulled apart more than 10 EarthBound carts.