I always thought a B-29 would be perfect, whether a plastic model or a metal miniature for the smaller scales. It is a pretty big plane so even a 1\72nd scale one might be fine with 28mm miniatures or there is a 1\48th scale one for megalomaniacs. swap the wings for something smaller, a 1\72nd Victor might be perfect doner for a 1\48th job, and chop the tail off and fit a rocket, atomic of course, maybe even a bit from an Airfix Saturn V as using it seems to be traditional for a lot of model work.
The Victor is a great looking plane in it's own right, a documentary described it as the most evil looking plane ever built. I wonder if my local model shop still has the Revell reissue of the Matchbox tanker version?