That was my first attempt at compensating for "the warp". Even added a bit of clear silicone in the middle. When exposed to gasoline, the silicone swelled, but still closed the gap in the vacuum to the power valve. I had to replace it a few months later, though. Second time around, I used a bit less for less expansion, which worked for a longer time.
After the two short-term fixes that summer, I ordered a Holley Variable Spec Manual. That book had the rebuild and parts specs for every Holley 2bbl ever built, up until about 1972. I used that to get the number for the OEM Chrysler Holley 2210 2bbl.
The Chrysler "Fix Kit" (for the Holley 2210) used an airhorn gasket that was thicker and softer than the normal airhorn gasket material. About twice as thick. When the airhorn was installed and then tightened down, I did it in normal torque sequence. Starting in the middle and working outward in a circular fashion. In sequentially-increased tightness levels.
The Fix Kit also had another item in it to replace the existing air cleaner stud. It was 3/8" square stock which went between the outer screw holes on the airhorn, with a new air cleaenr stud attached to it. Longer screws were necessary, too, which were in the kit. The short section of air cleaner stud was tack-welded to the cross-piece.
The cross piece also contacted two tabs near the center of the airhorn on the Holley 2210, pushing down on them when the cross-piece was tightened down. Putting downward force on the middle of the airhorn to flatten it out a bit. I'm not sure how something like that might be configured for the WWC3, though.
NOW, if you are up for a project, you might use a more modern "filler" like J-B Weld to fill in the gap between the airhorn and the throttle body float bowl rear edge. Key would be to make a thin line of the filler, then while it is still soft and workable, put a thin coat of grease on the airhorn and place it against the throttle body, with the filler in a thin bead on the top of the float bowl's rear edge. Squishing it out a bit as you gently torque it down. Once done, then carefully remove the airhorn and make sure the new rear edge looks good. This way, you can still use the normal air horn gasket and not need a spacer gasket situation, hopefully.
You might also get a straightedge and see how much warp in in the airhorn, too. Which can help gauge how thick to make that bead of filler, initially.
Rather than the J-B Weld, there is also a product to use to plug-up gas tank leaks. Like bubble gum, but a dries-hard sealer you can knead in your hand. Should be able to find it at an auto supply store. Once it is prepared, you just stick it on the outside of the tank over the pinhole, then let it dry. Might be more workable and easier to work with, possibly. Plus being fuel resistant, for sure.
NOT sure how ethanol-resistant it might be, but something like a tire inner tube piece of rubber to make another airhorn gasket out of? Lay the paper and the rubber gasket together between the airhorn and the throttle body. Then carefully torque things down, in sequence. The rubber might have enough give in it to compress and also seal the rear edge of the float bowl? And filling in the gap where the power piston vacuum passage is . . . which is one MAIN reason for the whole operation, to me. Keeping the carb on its normal mixture, rather than with power enrichment, at cruise and such.
Just some thoughts,