Custom page or paper size

Hello--I'm working on a project that will need to be printed on a custom paper size (6x9). I am having a very hard time trying to make this happen. I know (from Help) that I can supposedly set up a custom paper/page size. I've done exactly what it says, going through page set-up. But then, once I've got it saved, when I go back to page set-up, the option for my newly saved custom paper size is greyed out. I can still choose Letter, Legal, A4 or B5, but not my custom paper.

Any ideas?

Any other thoughts on how to do this? I must be able to output to a pdf that will be sent to a printer. If I merely change the margins, I'll still be outputting a 8.5x11 page size, though the text will be set to 6x9. I need 6x9 paper.

This is very frustrating and I've also tried to do this in Word to no avail. I had hoped that Pages, more of a quasi desktop publishing app could help me, but I'm really stuck.