ORIGINAL: Peter_OZ
I agree the Chinese and Vietmanese used them and locally build derivities as training / advanced trainers in their military arms.
If a Piper Cub can be painted green and called an L4 then it too is a Warbird is it not?
Even the De-Havilland Puss Moth can be classed a warbird as the RAF took over a few examples during WWII.
A standard Cub painted OD green is designated as an O-59 not an L-4 Grasshopper, but to answer your question, yes it is...