Holley makes high flow and standard flow power valves, but usually they are rated by their opening vacuum. When you say smaller, did you mean lower opening vacuum? Yeah, that would really screw up your tune. Most parts stores sell Holley power valves. I recommend getting the right one.
i read the packet my carb came in they told me if i blew the power valve i would be better off putting a 35 in it rather than a 65 but only when its cold it happens runs like crap and just keeps loading up when it gets to normal op temp it runs decent, but not at 100% like it should be i was thinking it might have dirt in the carb or rejetting it would help