Why are you wanting to put the 5.2 pod on the older car? Other than a little extra space for the motor, I don't really see it being worth the cost. Anyway, here's everything you'll need if you're adding the 5.2 pod to the original 12R5-

ASC4692 - Team Associated 12R5.1 LiPo Lower Pod Plate
ASC4702 - Team Associated Motor Mount Brace
ASC4688 - Team Associated V2 Upper Pod Plate
ASC4700 - Team Associated Motor Mount
ASC4701 - Team Associated Left-Rear Bulkhead
ASC4608 - Team Associated Factory Team Hub (Brushless)
ASC4609 - Team Associated Factory Team Thrust Cone
ASC4697 - Team Associated 12R5.1 Option LiPo Shock Mount Upright

Total cost @ Amain - $106.18, which is $3 less than the 12R5.1 lipo conversion kit, and around what you could pick up a used 12R5.2 for.

If you're just wanting more space in the pod, use an upper and lower pod plate from the 10R5 along with the ASC4608/4609 diff hub & cone to widen the pod to the same width as the 5.1/5.2. Much cheaper, and gives just as much width to work with as the new parts.