i have not made diptychs and trypych in the sense you are talking about, but i have had to print multiple images on paper that was later turned into signature pages for a book. the images had to be the same tone &C as if they were for diptych or trypych ... the way i did it was not very hard, but it was time consuming just the same. i took a sheet of paper that was going to be my "mock-up" and turned it upside down so i could draw on the back. i made a rough sketch of where the images were going to be with a pencil, and then i stuck the negatives in the enlarger, and made notes as to where the enlarger head &C was to make my life a little easier. i made a mask out of mat-board and just printed. straight cut matboard and bevel-cut board works well, but torn edges give a nice feel to the images as well.