Steering box question

[Jstock85]

I have an 85 c10 with power steering fluid pouring out. I need to replace both the pump and the box. Having already acquired a replacement pump I'm searching for the gear box. I would rather grab one from a local scrap yard versus paying full price for a replacement. I have several yards to pull from in my area with trucks ranging from late 70s all the way to the late 90s. My question is what year models is that part interchangeable with?

Any help is greatly appreciated!!

Jeff