EBP-1 PlansTruth be known, you can take the plans from a good R/C model of the EPB-1 and scale it up... then apply the principles, design conventions, and wood sizing from any similar proven, established homebuilt glider and you would be pretty close.
Contact the guys at the "scalesoaring UK" website, one of those people may have an actual set of "Real" plans, and if not I believe several people have drawn plans for large models.
When I was looking at a Backstrom plank as the basis for a homebuilt aircraft I found several discussion threads on the R/C model forums that showed plans, laser cut "short kits", computer renderings, etc.
The short span, thick wing section, and short load paths will make it a fairly safe endeavor to start with model plans. The wing ribs are absolutely conventional, standard issue, old-school stick-built ribs using 1/4" square spruce.