Greg this question would be better suited in the warbirds,kit building, or scale aircraft section, you will probably get several modelers who have quite a few resources on the D7, being that its a warbird and a scale one at that.

if you post a link to the drawings so others can check them out as well, you might get more engine size ideas, my guess would be a 70 4stroke for a model in that wingspan range would be a average to start with depending on your over all weight .

here is the comparable size ARF from Hangar-9 http://www.horizonhobby.com/Products...ProdID=HAN4675