Steve, you may want to check me on this but I do believe that with headers you will be a bit lean with the OEM fuel programming. Check Marc's web site as I think he has details on the page with all the EPROM descriptions and prices.
I know back in the old days a sbc 327 or 350 would run waaay lean on the back two cylinders on each bank with headers & stock jetting. It was sort of commonly accepted procedure that you had to step up the primaries 2 steps and the secondaries 3 steps just to start with and read plugs from there.
Tom