Yeah they are a pill. The old steel in aluminum thing where they just get too tight...guess it's better than falling out
I just did it the other day at a Stinger's house. Out of the 8 screws (top and bottom), I had one that required a little bit of brute force...
If you don't have a hand impact driver, then grab an old phillips screwdriver and smack the head good and solid with a hammer a couple times. That will usually loosen it up enough.
For the one stubborn screw that we had, I used a small cold chisel and gave it a nudge in the "lefty" direction. That left a little groove but the screw still works normally with a screwdriver.
Then when you get a chance, buy some metric allen head bolts at a hardware store. 5 MM, I think. Get stainless if you can. They are also easier to work with when the carb is installed, too.
If you look close here you can see the allen heads, top and bottom.