Eric,
I think what it means is that producing sketches with all the dimensions that you would require to properly replicate the numerous parts you need is more work than anyone is will to take on in one go. The request for paper rubbing to replicate the cam strikes me as impractical. Do you really think that is going to be accurate? There are other Aeros about, and sooner or later another engine is bound to turn up that would either be a more viable project to start with or a parts engine for the one you got.
But it does take time. If you want a project that moves along quicker, then you will want to look at something from Triumph, BSA, or Norton. There, folk are always buying and selling surplus parts and projects, due to the enormous production volume they enjoyed. With the smaller marques (and Douglas is not unique in this), the bulk of the projects and parts exchange hands through networking and word of mouth.
-Doug