I put my baseplates in a vise (wrapped in a shop rag), put a propane torch to the screw thread area & just dug at the brass screw with a little screwdriver and a pocket knife to "cut" a slot into it and the screws turned out easy once heated. It's a crude method, but it worked for me. Then all you need is replacement idle screws from Holley.

FYI- I have the adjuster tool/hex head idle screws and I don't see it as that big of an advantage since you still need a Promax base plate to get to the back carburetor. The screws are much less likely to strip out again though.