If you really think it's boiling the fuel in the bowls you might try a heat shield under the carb. Several of the BB vettes used them from the factory and that was back then. Could have been a performance enhancement or to prevent boiling the fuel
Several versions are available google "Holley heat shield".
Also depending on how long your valley pan has been in place they have been known to burn through but with a blocked intake I would think that added thickness of the intake would heatsink it away. but then again it may be heatsinking the intake enough to pass it onto the fuel line
I do know on one persistent b-tch, we made a base like the one shown, extended it to cover the entire length of the carb on the R side, then bending it downward to clear the fuel line while blocking the heat. 10 years ago and he hasn't had a problem since