Literally zero difference on 250-350. A 250 can have stiffer springs then a 350 depending on how it was optioned new.
All 99-04 fronts interchange. All 99-07 rears interchange. For about a 4in and ride quality you probably will want V code front springs, B code rears.
Call Trevor at PMF he will build the rsk to accommodate the wider track of the SD axles, and you will have options like receiver hitch, tow hooks, and more height.
Here is mine with the V and B codes
If you can tell from that pic. If not Ill find another.