There are a few ways:
Option A: two feed and two separate returns- both back to the tank. A bit extreme but it works.
Option B: call fI tech and ask them how they recommend since they built them.
Option C: “y” both lines just make sure they are over sized to handle the flow. Your idea of one unregulated flowing into the second is great but is a single 3/8” line enough flow for both at WOT?
I removed my single fI tech due to its inability to hold a tune, having to replace the regulator twice. And the O2 sensor once all within 300 miles. Tech service is not super but I’ve delt with worse. There is an actual website that a guy has on the fI tech sets ups where he covers all of the issues and has down loads and replacement part numbers so you can buy parts locally. Like the regulator was a VW Bosch part number and was better than the factory. Also verify the temp sender is good. It’s a Chevrolet temp sender but again in that website they give you a bunch of part numbers that are better.
