To you my advice might be a bit rash, I am sure it is because I still own one of this excellent glass :)
According to my friend Leo Foo,
"The Nikkor 300mm f/4.5 IF-ED was introduced by Nikon in August, 1978.
It was seen as an direct lens upgrade from the earlier Nikkor 300mm f/4.5 ED.
The Nikkor 300mm f/4.5 has a longer development history than comparing optic which can traced back as early as mid '60.
It has evolved not less than a few rounds of known upgrades."
The Nikon 300/4.5 IF-ED is a very compact lens for it's 300 mm focal length.
It was very popular in the 1970 and 80's, I remember fondly that it was a standard issues to Reuters photographers.
While working in Singapore newspapers in 1994, I went to see a Mr. Lam at the Nikon outlet, in Center Point.
I was ecstatic that he kept a BRAND NEW IF-ED for me! Thank you Mr Lam!