That's such a cool looking plane. A guy in our club flies one occasionally - looks fantastic cruising along slowly overhead. Downthrust does work, but down trim on the elevator does too, if you have enough available. As I mentioned, I increase the incidence of the stab on old designs when I build.

Some planes have downthrust even when they don't look like it. My DeBolt Champ doesn't look like it has any, but if you look at the wing angle, and the elevator/stab (after putting in enough down trim to make it fly straight) and ignore the fuselage, you can see that it actually does have downthrust. Jim