Awesome - looks like you know what you're doing. I said regulator, but I meant it for use in the over pressure safety sense. Looks like we have basically the same build. I'm doing a Redeye with Tremec Magnum in a 70 Cuda.
Have you cross referenced temp between your gauge with the probe in the tapped housing, and the ecu temp reading? I was concerned that the gauge wouldn't report temperature until the thermostat opens, or does enough fluid flow through the tiny thermostat bleeder hole to give you an accurate...
Fore Innovations makes a Y that has female -12 ORB ports with the duals running parallel. You would buy the fittings that adapt -12 ORB to -8 (in your case).
https://www.foreinnovations.com/product_p/19-001.htm
What's your plan to drive the dual fuel pumps? Can't see it in the pictures, but do...