You only need 2 plains/sprites per reel to do this. Set your image sequence up in 3 arrays, one for each reel. For each reel:
1. Texture Plain 1 with image 1
2. Texture plain 2 with image 2
3. Scroll plain 1 down, hiding behind your facia (another sprite/plain) as it goes.
4. Scroll plain 2 down, appearing from above, behind the facia again.
5. When plain 1 is out of sight, texture with image 3
6. Move plain 1 to top
7. Repeat, taking account of new positions.
I did this years ago (1993 to be precise) for a digital clock...on a mainframe with text only output!!!
