Glad you got the Stead alloy enricher cable coupling installed, mrsteve!
Now, about FASTENERS.
The carburetor machine screws have JIS (Japanese Industrial Standard) heads, NOT SAE Phillips heads. You can get a better grip on these with a JIS bit; however . . . even so, Galvanic corrosion, between the dissimilar metals (steel machine screws and alloy carburetor body) can result in tremendous adhesion.
An IMPACT DRIVER may be essential to remove some stuck screws; or, judicious application of Vise-Grip pliers; or, cutting a flat-blade screwdriver slot in the screw head with a hacksaw or Dremel Moto-Tool . . .
After that's done, a good idea is REPLACING all external carburetor screws with Allen-head (hex socket) screws, for increased torque. Anti-seize compound on the threads isn't a bad idea, either. Eagle Mike sells an inexpensive kit of Allen-head carburetor screws.
Again, congratulations on solving the starting enricher cable puzzle!