Extended side-frames and back rest

In an effort to improve the stability of my Peter Lynn Comp XR+ kite buggy I am after some of the heavy duty extended side-frames, I know I can get these new but does anybody have a set they don't use?

I am probably going to get some as a birthday present! The other option is if anybody can fabricate a frame extension to join the side frame to the axle?

A backrest from A Wind of Change

The other thing I want to do is make a back rest, for comfort and I reckon it would also stiffen the frame - I know Popeye the Welder can do this but I don't have the skills! I think I will take a trip to Masters or Bunnings to see what I can botch!