spar mod, -3,-3A, -3B.
I have a -3A with the original Change notice CN-1-2 for root rib modification. THis mod has upper and lower 6061 angle and 1" x 1/8" flat bar riveted to the fuse/wing root ribs ( L&R). Requires re flight testing and noting placard on the panel that the aircraft has been limited to _+ and _- G's and is not to exceed.
CN-2-1 requires the wing skins to be removed to have access to the rear spar stub and is a bit of work to comply with. It is mandatory for aerobatic flight..
CAll Vans and ask for CN1-2 and CN-2-1 drawing package.
hope this helps