Fuel Pressure is taken after the fuel rails. The fuel first goes into the passenger side fuel rail, then thru a connecting orface, into the driver side fuel rail, then the pressure is taken. Connections to and from the rails are large so no pressure lose is expected. But me and my brother feel that it is possible that the fuel pressure on the passenger side could be at least 2psi higher than the driver side due to the connecting pipe between the rails.
The pipe is small and could be considered restrictive. We are going to take the pipe out tomorrow and measure the ID and plug it into a bunch of equations to see exactly how much the pressure could be effected. I would like to know has anyone already done these equations, or actually tested how much the pressure is effected, and how to eleviate this problem if it does exist.

 

I didn't bother with the "equations".... just "split" the rails and feed each side independantly from the back, and take the return off the diagonal cross-over pipe in the front. Pressure gauge tap is on the rail between injectors #4 and #6, and that is pressure measurement used to adjust the AFPR, located at the cowl. This system, using stock LT1 rails, has supported over 1,200HP (obviously not on my car, I'm only at 800 with dry nitrous) with no evidence of differences in fuel distribution from cylinder to cylinder. Later versions of this setup are configured with a separate return on the front of each rail, rather than using the cross-over pipe.