All the Holley floats I've ever seen adjust by a nut on top of the float chamber, no need to take the bowl off. Just loosen the screw above the fuel inlet fitting, and turn the nut under it right or left to raise or lower the float level. Clockwise raises the level, CCW lowers it. The plug in the side of the float bowl is removed to watch the fuel level, and it's right when the fuel just barely trickles out of the open hole. I've used a 350 CFM Holley successfully on a 358 cubic inch Chevy engine up to 6,000 RPM on a round track engine, so the 500 might be a little over-carbed unless you're racing.
Jerry
