John, using selected balsa for the spars would be more than enough strength for this particular model. I'm not saying that basswood wouldn't work, but its adding unecessary weight. Once the center section of that wing is sheeted it becomes somewhat unitized. Just use the maple for the mounts and only as long as you need them. Generally, even if the plans call for a certain size plywood doubler, I decrease by a 1/32 just to save weight. Anything you can do from selecting light grade wood to sanding to glue application will help this model benefit in its flying characteristics. Ken