Looking through the manual, the brace actually just supports the wing against the fuse.

If I understand correctly, in a bipe the top wing produces a lot of lift and if it were not properly supported, the top wing would just break in two or break off the fuse. In the real thing they actually use the wire bracing to tie the upper wing top the lower wing. This may appear to have a bit of slack on the ground but once in the air, the wire bracing tightens up as the top wing tugs on it.

Now coming back to the Reactor Bipe model, there is no 'screwing-in' the top wing to the brace. You just have two dowels in the top wing that go into slots in the wing brace when you assemble. There is no physical assembly between the two other that that. So, the brace is there for aligning, providing a route for the wiring and for supporting the wing- it acts entirely in compression and the real load is taken by the wing struts that you screw in both sides of the fuse into both top and bottom wing. So, technically I can use just a polustyerene block -they are good in compression as I would be using blocks used in rooftop insulation (capable of taking 750kpa if I am not mistaken)- they are samp;es provided by vendors and its called 'XPS'.

Now hold on a minute before the readers get any wrong ideas. I have another Reactor Bipe which is still in the box and it has the brace. I am looking to see if I can get someone to replicate it for me so I can use on this airplane. If I cant find a source, I can make in polystyerene and then fibreglass over the top. I just dont want to use the brace from the other model right now and pass the problem onto when I build that one

Ameyam