I think your 4.6 stock unit is 77mm in 99 they went to 80mm. The lightning maf's are 80mm and 90mm depending on the year you pickup. I believe it's 2000+ models that have the 90 maf. Remeber Maf's from Cobra's are calibrated for 24lb. injectors and the Lightning maf is calibrated for 42lb. injectors. Not a direct swap with a chip to modifiy the fuel tables.

Who cares what size maf those dinosaur fox's use