The carb pan is plastic, not fiberglass. Your idea with the wedge is right on, and would work for sure without sacrificing clearance between the top of the carbs and the bottom of the pan. However, since the sides are tapered, there would be a step on the inside and outside. I've heard this type of plastic can be heated and formed quite easily, but I fear if I try that I'll end up with an ugly plastic lump.

Yes, they make metal pans. The plastic one is $130, metal $369. When they're painted black, there is no way to tell if it's metal or plastic.

I'm hoping someone knowledgeable of working with this type of plastic would chime in and give me some ideas.

Tonight, I'm going to cut the bottom carb connections as described earlier. I'll report back on how much clearance this creates.