A lot of guys put a ball bearing in the vacuum hose for the distributor. Looks stock but curved for performance and they don't want vacuum adv. Frankly this is the same here. Easy to install an orifice in the return line or block it. The real issue is running the carbs with no filter.

There are metal gas line filters with a return available. Not oem. Or run a standard filter.

Someone should get one manufactured as a real filter with a blocked return.

If you're not running the brass screen at the carb inlet fitting and running this separator with no screen you are running the risk of junking up the carbs especially idle/transition. All for the OEM look. Show car not driven fine, a driving car not so good.