Funny thing about guitar:
I am left handed. I play a standard guitar, neck in left hand. I have since the late 1900s. I've taught several right-handed people guitar, more than half of them want a "lefty" guitar to put the fretboard in their right. At least one was willing to try to play a normal guitar upside down, not restrung Jimi Hendrix style. So I'm not convinced we don't just have guitars backwards.
I made the transition from trumpet to french horn just fine as well.