A little help here for fuel line set up. Ive got a 1999 L67 with aeromotive fuel rails, how do I plumb this into the fiero fuel system? Do I need a return line or not?

Yes, you will need a return line. The regulator must be after the fuel rail.
There are two options:
1. Have the fuel go thru the rail and then to the regulator.
2. Have the fuel rail tee off of the line going to the regulator.

You must use a vac/boost referenced regulator with the outlet going to the tank return.
Some regulators meant for option 2 already have a tee built in and have 3 ports, one in from the pump, one out to the rail, and one out to the tank return.

Hope that info helps.

Ok so I need to run a line from the tank to both fuel rails, then both back out into a regulator, then back to the tank. Is this correct?

There are a lot of options for how you hook up the 2 rails to each other. That part isn't as important as the regulator routing.

There's a recent thread with some diagrams and more info here.