There isn't any point in getting upset with the cummins folks. They do their job, and quite honestly, their job description doesn't include helping you put together a mismatch of parts. They don't have any more information than you do, and quite probably, less. Cummins builds engines to a particular customers specifications, and sells them. That's Cummins with a capital "C". Corporate engineers do that, not Hadji behind the parts desk. There are literally hundreds of possible combinations, and if you don't have specific knowledge of something, you aren't going to find it in a parts reference.. All the guy behind the counter has is the CPL# (control parts list) and what parts go on it. You need to check with a medium duty truck shop for that particular conversion. Gun512 is correct in the fact that you should use an SAE 3 or SAE 2 flywheel housing, as the 3053 from a duece already has a bell housing to mate to it.
What you are trying to do is cool, but it is a puzzle that you have to figure out yourself. Holding some guy responsible because you don't know what you need is pretty much ridiculous in my book. I understand your frustration, but if you want it, gotta pull them britches up a tad and do it yourself.
Doug
4btswaps.com is a very good resource for various bits of information as well, but I can't say that I've seen the specific question answered there. Still wouldn't be a bad place to look, ad there are a few swaps over there using SAE type bell housings and transmissions.