I'm wanting to lay my seat back further in an existing pitts S1-S. This
would require moving the tube at the top of the seat back, back about
2". This member is 3/4 x 0.035 and about 22" long.

I was thinking to run 4" long gussets back to the original attachment
point, creating a C shaped section.

The problem is that the center of the tube now dosen't line up with the
centerlines of the other tubes at the cluster. I know this has been done
before but I have no idea how to work out the size needed for the new tube.

Does anyone have experience with this?

Regards

Martin Morgan