FWIW here's a US market F150 plow doc showing some weights across the line up.
If desired s/b able to order a higher rated spring from dealer parts. I've done that with my SD, was pretty easy to install. Or aftermarket with or without a shock. Or talk to that local spring shop ...
Not to say I wouldn't order SPP just for the upgraded alt.
Thank you Klahanie. I took a look at the SPP package body builder guide and then compared that to the body builder guide without the SPP package and there doesn't appear to be any difference in payload.
What I did discover is the 5.0 offers 500lb more GAWR on the rear axle (3800lb vs 3350lb) and 120lbs more payload 1840lb vs 1720lb.
That much of a difference on the rear axle alone seals the deal. 5.0L it is!