I think Luke = Tail/Dais and Chewie = railing/hookah
It's actually Luke = railing/hookah and Chewie = Tail/Dais 
OK, so then:
- 3:12 R2 always comes with Jabba's torso
- 3:12 C3PO always comes with Jabba's head
- 2:12 Luke Skywalker always comes with railing/hooka
- 2:12 Chewbacca always comes with Tail/dais-right
- 1:12 Amanaman always comes with dais-center
- 1:12 Bib Fortuna always comes with dais-left
So, if you buy a box of 12, you'll have:
1x complete Jabba w/dais
1x Jabba w/hooka (only 1 dais piece)
1x tail-less Jabba (Head and torso only)
And, if you do pick up both chases, you could use those parts to complete a second full Jabba w/dais. That would help you recoup some of the cost of the chases I guess...