It is not uncommon to have the root doubled in 7th chords as with triads. So you can have the 7th both above and below the root. There is definitely a 3rd inversion for seventh chords that puts the seventh in the bass and this is not at all uncommon in guitar big band chord voicing. Older books on this try to place the "lowest" note on the low E string while moving as little as possible. I am not sure this is for harmony reasons as much as for simplicity of hand movement for very fast tunes. These two basic rules taken together generate very "interesting" voicing and movement for the guitar. However, as you may be aware, in the big band era (pre 1940s) the guitar was more of a melodic drum. So it's not clear that the choices made would survive today.
That being said all I can say is that putting the 7th below the root is no at all bad. The real issue would be the stacking of notes and to that end I'd say you want to avoid small intervals in the bass. So if the 7th is below the root I'd bump the root up an octave to create some space. There is a concept in guitar voicing called "fat chords", I'm sure pianists use that term too. The idea is to create a large interval between the bass and tenor voices and allow for a small interval (3rd) between the alto and soprano voices. This goes back to classical four voice harmony theory.
In guitar chord melody there is a voicing of the Maj 7 on the upper 4 strings that goes like (x, x, 7, 3, 5, 1), two 4ths separated by a minor third. It is particularly easy since the (7, 3) and (5, 1) will be on the same fret.