4bt/GM Transmission
Have you searched the Cummins/Diesel Conversions forum on this site? GMs are usually an easier swap. What engine/truck/drivetrain are you using? The reason a Chevy is easier, is that GM used the Cummins 4bt in their P series bread vans. They usually came with a Turbo 400 automatic transmission so you have great flexibility in transmission choices.
The 4bt in those vans has a different bolt pattern on the back than the 6b. These parts are interchangeable between the 4 & 6 cylinder engines. This means almost any GM transmission will bolt right up. The 4b may make it easier as far as engine mounts as well. Only thing with using the 4b transmission is that it will be mounted at an angle.
Try Jamie Avant in Georgia for adapter parts, he sells a kit. Check with cumminsstuff.com as well. Check the other forum, there's plenty of info there.