I saw the box art for the MPM 1/72 Douglas DC-2 Bomber and thought that the concept could be used on the DC-3 all the way through to the DC-7, although I would love to build the DC-5 (the one with the shoulder mounted wings).
The MPM kit comes with the bog standard DC-2 without the interior seats and resin parts for the bomber conversion- two different nose guns, upper open turret and under wing pylons.
With the Alleycat turboprop improvement sets this could be taken a step further although there's plenty of engines to choose from.
I haven't seen the bomber conversion set sold separately, so I shall be buying a few of these kits for the Revell DC-4 and the Heller DC-6B.