Could there be a typo in the title? He's saying a 99 F450 with a SRW 3.73? I'm not aware of any F450s that came with a single rear axle, and none of them were 3.73 gear ratio.............
How many 99 F450 4x4's, with any differential you choose, have you seen?
2000 F250 Lariat CC SB 4x4 PSD Auto