I've used Polly Scale CDL straight out of the bottle and mixed Tamiya paints (deck tan, white, various yellows. I can't rememember the formula, but may have it written down somewhere. Your mix sounds just as good and my method sounds very similiar to yours also. I preshaded the locations of ribs, longerons, etc., with dark brown, sprayed a thin coat of CDL overall,  then went back and masked the areas between the wing and empennage rib locations and sprayed the ribs with a lightened version of the CDL that I originally used. This photo of a Be-2c gives a good illustration of what it should look like:

http://www.flickr.com/photos/judgedredd76/2374780910/

WWI rotary engines had total loss oil systems, were notorious leakers and smokers, and usually after a only a few flights the forward 1/3 and entire underside of the fuselages were saturated with burnt castor oil. Be careful because some French aircraft that appear to be CDL were actually painted in a color that resembled CDL(????) and some  German aircraft appearing to be CDL were painted white or very pale blue/gray. If you can't tell from photos just go with whatever you like. WWI color interpretation has a lot of leeway.

Here's a link to a nice selection of Sopwith Pup photos:

http://www.flickr.com/search/groups/?q=sopwith%20pup&w=41806985%40N00&m=pool...

yes Humbrol still make it #74

WOW !!!

Should this discussion be stickied as a necessary technique for our niche?

Agreed...I have an idea...PM in bound...