When you say 'SVT MAF' I'm assuming you are referring to the black plastic body MAF? Put your old aluminum MAF back on. There is no SVT-specific factory MAF. There is, however, a specific MAF for all 2K Contours, because it was Mechanical Returnless Fuel, which did have different injector specs and MAF calibration curve compared to the standard return system used in all other Contours. But for any given model year, the same MAF was used in both SVT and non-SVT V6s. I tried this myself when I put the conical filter in my '99 Mystique, along with the attached plastic MAF, and it threw a P0171 in 5 minutes.
Did you also reflash your PCM with the SVT calibration when you went to the 19# injectors? If not, you wouldn't get a P0171/2 lean code set, but you probably aren't taking full advantage of the upgraded injectors.
