Oh, I thought that you meant the round-nose B-18
, which obviously had an extra-long session with the Ugly Stick.
The pedigree of the B-18 is somewhat confusing given that it was developed at about the same time as the DC-2 and -3 were. It's got a C-39 tail, DC-3 wing, DC-2 fuselage but it has an entirely new lower section to house the bomb bay and also the new nose section for the guner, bomb-aimer and other crew to sit in. Douglas was branching out in all sorts of directions at the time, which from the perspective of looking back and expecting an orderly, linear, evolutionary development process make exactly no sense.
I've built the SH DC-2 which is a very similar kit, and had very little trouble with it. You need to have some familiarity with short-run models given the complete absence of locating pins and the sometimes frustrating breakdown of the parts (separate prop blades and hub, anyone?) If you have any amount of experience, I'd say that you'll enjoy building it
There are a few online builds of the Digby boxing which you may not have found if you were searching strictly for "B-18". Many of them are suffering from Photobucket's infamous ransom notice though