90 Suburban 1/2 ton rear springs

[shawndzugas]

I know that most 3/4 and 1 tom suburbans for my year came with 56" rears. my 1/2 also has them. does anyone know if this was part of a towing package or heavy duty 1/2 ton? Or did chevy use the 56 and 52s interchangeably for my year.