7875 + 5.9 + E85 + Megasquirt

The older Edelbrock rails like the ones I have were NPT, but yes, they are sized for -6AN. The other thing would be is if the fuel goes through a Y block and to both rails and then back to the regulator which bypasses to the tank. If its one rail to the other it seems a lot more likely to go lean on the 2nd rail.