The TH400 version is the GM Kit.  You do not have to have TH400 transmission, but rather the NP 205 that has the big input bearing. 90MM or that has a female input gear (TH400 version of the 205).

This kit is made from three pieces:

The TH400 kit is made from three pieces: The fig. 8 bolt pattern is welded to the ring, and then machined flat. The ring that is welded to the 203 plate has a dia. of 7.5″. With this diameter the ring is aprox. 1″ from the bolt circle. Providing a very strong adapter.

The TH400 doubler kit has an oil seal included and installed to keep the fluids separate. There is also a vent hole with a 1/8″ pipe to barb fitting included. This is for the venting of the NP203 only.

I can set the rotation of your 205 to what you want… But the two most popular is either stock or up 2″ or 12 degrees…