I assume you are talking about a PDF magazine ( 60M is an average magazine size).
You just move it from your PC directory to the iTunes area, then you move it in iTunes to the Device area.
It will show up in your iBook at the PDF library.
I do it dally. ( A local free newspaper + Some Magazines from time to time)
Once it's in the iBook, I delete it from iTune. Don't need it there. The backup on the PC directory is good enough.