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but when I was originally going to run the setup, he told me that even a single Holley/Weber would be an improvement over the original 1 barrel. I'm dissappointed that he would tell me that and then tell me about the power loss after I made the purchase.

I've heard a few others say the same thing,a single H/W has less part throttle power than the single barrel,but usually more power when wide open.I believe that the seller of these carbs does does not tell customers that unless they ask him directly.
I guess you may have not gotten exactly what you wanted.