Suspension Options Other Than Parabolic Leaf Springs?

[mog]

I know this is probably a newbie question that has been asked and answered many times, but 37-13.5-17 tires will fit in the stock wheel openings without have to add new springs with a little lift? I would prefer to wait until the flatbed is built before having custom springs built, but I was just under the assumption that with such a bigger tire I would need new springs to replace the tired and sagged originals and or to lift the truck for tire clearance.

On my stock suspension 2002 FG my 37s fit with zero issues front and rear (box truck body). [right around 100k for miles, it was a furniture delivery truck in Colorado prior to my ownership, no heavy loads, so I would guess, little to no 'sag' on the stock suspension]