The book is 8" x 11", the standard size for US gaming books. However, my laser printer prints on A4, which is 11.7" x 8.3" -- so slightly larger. Not much of a problem: most printer drivers will happily resize for you. However, I was thwarted by the way printers work.
You see, a printer needs to 'grip' the paper before it can pull it over the drum with the heated toner. And the toner is not large enough to print at the very edges of the paper. But that grip-area means that a print will always be off-center: the non-printable area at the top is always larger than the non-printable area at the bottom.
That's not too much of a problem, but if you want to print on both sides, you will get a slight shift. For stuff like letters, that's totally not a problem, but for a sheet that you need to fold, it is. It means that the fold is not in the middle of the sheet, and that one page is shifted either left or right.
Humans are created to detect symmetry, so an off-center fold like that is immediately apparent!
I spent a few hours working on this, trying different ways to position the prints on the paper, trying to trim the excess margins so the fold would be in the middle... nothing really worked.
So I'll just be printing the book full-size, and use the lumbecking machine to make it into a book... It's not ideal, but it's the best I can do at the moment.