Leaf spring question

['79squared]

Is there a way to tell which factory size I need? (52"/56")
My truck has no factory stickers left on it and I know for a fact that the rear leafs have been changed because I did it. Then like a dumb dumb, I chucked the old springs because the PO had heated them to lower the truck rendering them junk. So I went to a junk yard and picked some up used not thinking about measuring them. Right now I have 56" springs but I want to put brand new springs on and am not sure which size.
I guess another question is, what size (52/56) and how many (3/1, 4/1, so on) did my truck come with. 1979 c10 shorty custom deluxe.