With the GM adapter like you are refering to you can basicaly bolt up any GM trans to the adapter. Mine would even allow a Buick, Olds and Pontiac trans. Manual or auto will work.
I have a 4L80E behind my Dodge 6BT with the bread truck adapter. It works great.
The trans behind the Cummins in the bread trucks are special, but any other GM trans will bolt up inplace of it.
The engine is just a 4 series Cummins Nothing special. It is kind of like a Chevy 4.3 v6 is to a 350. All the bolt hole dimentions on a 4bt or a 6bt are the same.
I see the adapter plates all the time on ebay and one seller is selling a billet adapter and flywheel for $1400. The bread truck versions are $750 and up.
BTW my truck is for sale on ebay right now search GMC CUMMINS its a blue 1996 CC 4x4 dually