Hi group. I am in need of some information.

I am looking for a very specific application adapter plate. Some 20 years
ago, a number of Chevy P30 delivery vans were factory repowered from gassers
to 4B Cummins engines. The adapter plate was designed to bolt the Cummins B
block to the TH400.

Now question being, Does anyone know if the adapter was a GM part or a
Cummins part? Or has anyone ever even heard of this piece? I am searching
for one.

thanks.