Plenty of people have an F250 or F350 with Cummins power. They had to make it themselves. www.fordcummins.com
is one of the bigger companies selling adaptors. It's not cheap but if you have a 6.0 powerstroke engine that needs work or a rebuild you are talking big bucks either way. Those guys even sell adaptors to use the allison transmission if you want to get really sophisticated.
Nice winter project for those DIY mechanics out there.
The cummins 5.9 has powered much larger vehicles like school busses full of fat children. It is very overbuilt for anything in the 3/4 or 1 ton pickup range.