Have you joined the wing halves yet? If not you can make a center rib with a
tung on it and reinforced the bulkhead and cut a slot for the tung ala the newer
LT-40 ARF way. I had mine from 1/4" aircraft ply and once the estimated slot
height was cut, I filed the slot till the wing fit very snuggly with very little pressure
on the wing when the bolts were tightend down. It is a lot easier than drilling for dowels.
Let me know if you would like pics of my set up. The pics below are my LT-40.