The Holley two barrels never really made a good street carb, always had to be messing with them. I agree with 34-40 on the 600 Holley being absolutely dead on perfect for a small block Ford. Granted it's overall bigger then the 500, but remember it's a vacuum secondary 4 barrel so at idle and normal driving it's just a 300 CFM two barrel til you stand on the gas and the secondary's come on. That good old reliable 1850-2 600 cfm, vacuum sendary Holley is absolutely perfect for a small Henry. Heck, I've got one on my pickup with the 351 Windsor in it, still works great with the added cubes and a lot more weight. The Holley two barrel can be made to work, but no matter how you do the tune on it, seems you're always sacrificing idle to support the transition and top end circuit, or vice versa. Just never had good luck with them.