A lot of the pages are a bit too tall and/or too narrow to fit in a standard frame. If you don't want to get custom mats, here is what EcoCycled has come up with as a creative solution:
1. Get a floating glass or magnetic acrylic frame that is a bit bigger than the whole page and doesn't require matting.
2. Take a large sheet of colored craft paper that complements the printed page and put that behind the page. Put the page in front, and then put them both in the frame. You will see a bit of the colored sheet showing around the edges where the page is a bit too small. You might need to crop off some of the top and bottom of the page to make it fit. This lets you see the whole page, including the edge where it was removed from the book for an interesting look. If you don't like the rough edge, you can trim it off carefully with a paper cutter, and then do step 1 above.
3. If you don't have the right colored paper, or the colored paper isn't big enough, we have a slightly different solution. Take the backing board from the frame and paint it with a complementary color around all the edges that will then show through. Or use a heavy piece of paper that you paint to put behind the page if the backing board needs some thickness in front of it. Then put the printed page in front so that the painted border will fill in the space where the page is too narrow. Crop the height of the page if necessary (or you can fold it over if you don't want to cut it). Again, you can leave the rough edge to show the full book page, or you can trim it carefully with a paper cutter if you want a clean look.