I'm running a mild 350 with a 700 cfm holley double pumper, the carb does not have a timed vacuum port, so how does the vacuum advance really work? Does it take ten degrees out when at full vacuum? What should my timing be set at?:thanks

The timed port is on the side, in the metering block. Have the original Holley metering blocks been replaced with something else?

The vacuum advance "advances" - it is not a vacuum retard. Whatever the mechanical timing is doing, vacuum adds more to it. When vacuum drops, the additional advance is reduced. At low vacuum conditions, such as wide open throttle, the vacuum is too low to add and advance.

So is there a way to set up the vacuum advance or do I need a new metering block?

If the Holley is the way it was from Holley, the timed port is on the passenger side in the metering block.