176 back issues of sci-fi mag "If" available on the Internet Archives
If Magazine at the Internet Archives. You can read online, or download in various ebook formats as well as PDF.
Not much I could add. I remember reading it as a youngster, before it merged with "Galaxy". I thought of it as a second-string magazine, behind "Analog", but it had several good years when Frederick Pohl was editor.
I'm looking forward to reading them. You know how it is with the old sci-fi magazines: Lots of forgettable dross with the occasional classic gem, and a window into a particular era in the pop culture.