Holley Float Bowl Leaking after rebuild

I have the same problem with the 1920 in my Dart. Drips a little bit when it's been sitting overnight. Apparently it's the carb body that warps, not the cover. There's a video on Mike's website on how to de-warp it using a torch (video shows a different carb, but the caption says it applies to the 1920 as well).
I haven't tried the torch trick yet.