That is certainly thinking out of the box. While it may not be a fast swap.... it will certainly get pretty good fuel economy. I hope that your 5th gear is tall.. or you run 3.08's out back ;)

Problem with a Cummins swap is the weight and they are so damn tall. Duramax would've been cool.... The ALH will be a trip to drive.

I gotta give you props for doing all the body work and rust removal/repair. I would've run in the other direction and not looked back.
My built LS7 gets low 20's on the highway driving like Ms. Daisy.