I'm working on swapping an F20c into an old 510, but I've run into a couple of issues.

1: Do I need the factory dash/chassis looms, ignition, and immobilizer to run the car. I am hoping to run the stock ECU until I have the funds for an AEM or Haltech standalone unit.

2: I was hoping to have some old-school dash gauges in the car, what's the easiest way to do that considering the not-so old-school stock dash setup.

 

Your best bet is to use after market management. That way you are not worried about the immob. Getting the dash harness might make things easier only for the C101 plug off of the engine harness. Im not sure about the gauges but the easiest route would be to install a S2000 cluster. Unfortunately its hard to get the fine details with F20 swaps online.