I don't believe there is any difference in frame length. You are right that the radiator is clear to the front of the frame rather than back like it is on the 4 cyl gas. The frame on the left side (from seat) of a diesel tractor has a section where it is bent down slightly to allow for the injector pump to fit.I can't seem to find any specs on the frame lengths but I did talk to a guy one time that was in the process of doing this and I remember him saying something about a clearence issue on the front pulley, I believe he altered something to make it work. As far as the hood if you look at a pic of the 45D the grill and radiator are moved all the way to the front of the frame this would account for the longer hood.
Just my 2 cents for what it's worth.
In the middle of helping my dad fit a engine from a gleaner combine into an original diesel tractor. I believe he said from a C gleaner. Should be a fun project.