My very first radio 40 years ago, I ran the cutter across the top of the box. The manual sat just below the top. Cut a line straight through the first few pages !
Sweet radio...congrats! Yes, ALWAYS save the boxes and packing inserts. They are the best protection for shipping the radio for service if need be and selling later. I take all the manuals and paperwork from my boxes and put them all in one handy, easy to get to file folder. I then pack the little boxes inside the bigger boxes to keep things compact. And then I store them in a safe, dry place in my attic. Keeping boxes can be a pain, but they ad appeal when selling and there is nothing like them for shipping!
