Since you are looking for something to test your tool on, I was going to suggest you to do it with the whale I've imported for OHII...
...but then it came to my mind that the whale got animated meshes. How is going GR2 editor to deal with them? In s3d this process was automatic but now, I guess, each mesh should be imported manually. Furthermore, the dat format had a MeshAnimationData controller, but what about GR2 format? I cannot think of any GR2 animated object featured in SH5 (flags are still in dat format by the way)
Okay, just talking out lout. Time to shut up and wait for your answer... unlike me you at least know what we are talking about