67-72 power steering

[davano]

I know this question has been asked and answered before, but I am unable to find an answer now when I need it. What years of power steering gears and pumps are a direct bolt on replacement for my 1968 1/2 ton p/u with manual steering? I've heard up to 1978 and I've heard up to 1987. I am preparing to do a swap for my manual steering and have factory 68' brackets, but rather than try and locate a 1968 pump and gear, I'd prefer to get a later one from a wrecking yard if that works.

Thank you,
David
Oregon