Orion that's the fun part i remember from making my truss scope.
As a double truss with a mid mounting point getting the balance made it even more fun
There are programs around that have been written to calculate the lengths and balance points for truss scopes but i found them even harder to work out .
I used Newt 2.5 first to get the overall length and then using a weight set set up a balance beam and mounted components on the beam except for the mirror and just adjusted every thing untill I got the balance while keeping the over all length the same.
This workd out for me.
But every one has there idea that they hope will work for them.
Good luck with scope.
Mark