Lower / Dropped Rear Spring Identification

[drbeeper17]

I'm hoping someone on this forum can help identify these rear springs from my 1969 C10. I bought a rolling chassis with these installed, but the previous owner did not know how much drop they were for. I don't care about manufacturer, rather just how much drop they are for. I'm guessing its somewhere between 2" and 6", but I really don't know.

They have been painted, and the only marking I can find on them is a stamped R4. They measure about 10.25" under no load as seen in the picture. Installed, the truck sits pretty low with only a few inches between the frame and axle (and that's with just the bed floor installed).

Thanks!