The LA .40 would be a fine engine on a DD. If you require a little more top end after you get dialed in with it, the SPAD to the BONE web site has a great tutorial on how to make a mousse can pipe. I made one [for a LA .40] and got a 1300 rpm jump with a 11x4 prop, I imagine the increase with a 9x6 would be even more. A 9x6 prop would give this combo good speed and good vertical without working the engine too hard. Figure on about 15-16,000 rpm. A 10x5 would be a slightly slower option.
Have someone with experience take it up and get it trimmed if you can........or have a helper ready to dial in your trims while you keep your eyes glued to the plane. With a real good inspection for any twists or warps after covering the model, it is possible to maiden a plane that isn't too far from perfection. The CG with tailless planes is in a narrower margin, but not so narrow that it can't be checked on a pair of fat finger tips.