Holley 600 dp jet help

A vacuum gauge can/may be used to help tune the low speed circuit, and specifically the idle circuit,but nothing more.
Your carb has several more circuits.
Try not to be overly concerned with a specific vacuum number, because, by itself, it reveals very little to nothing about mixtures.Ignition timing has a much bigger effect on the specific vacuum number than fooling with the mixture screws.
If your carb is not factory original, you may have to tune several other circuits and things.
If your carb is factory original, it will be pretty close, but may still require tweaking.
I think I read a very good article on the Holley website.