Next install the sealing rings on the center support. These are usually iron rings. I use teflon. Notice the 2nd ring is omitted. This is part of the dual feed mod also used on TH350s and TH400's. Install all three rings unless the trans has a improved forward drum.
Install the thrust washer on the back of the support.
New lip seals on the OD side. Be sure you get the correct seals, they can be confused easily with others used in the trans. The ATSG tech manual covers the difference.
Install the center support in the case and be sure to line up the fluid passages on the valve body side. Install the center support bolts.