This swap features two out of 'four ways to slice it.'The approach for all four of your post cards will be COLLAGE. You may enhance each collaged post card base with other mediums or techniques to complete it.
For your first and second card: SLICE & ALTERNATE
Full sheet of glued alternate strips
2. Then line up the strips, alternating every other one, on a piece of 8+1/2 x 11 cardstock, side-by-side in the order the images were originally arranged.
4. Glue them in that position (one strip at a time), alternating strips from the two pictures.
ALTERNATIVE option: use a full sheet white label sheet with the sticky side up on which to arrange your strips, but be careful- if they get snagged before you position them, your strip(s) will be ruined.)
3. Shift every other strip up (or every other one down) about one inch, taking care to visually line up the images of every other strip horizontally, see shore line in example.
4. Glue them to a full-sheet piece of cardstock in that position (one strip at a time). (I don't recommend label sheets for this more complicated arrangement.)