Another thought: you can keep the guitar in CGDA tuning, put a capo on the 7th fret, and have GDAE and a scale-length and fret separation that's closer to a mandolin, plus you'll be in actual mandolin/fiddle tuning, not an octave below.
Tenor guitar and tenor banjo are equivalent CGDA tuning to the mandola/viola, but many now use what is called "Irish tuning" or GDAE like an octave mandolin. As stated above, different string gauges required.
Gibsn: '54 F5 3pt F2 A-N Custm K1 m'cello
Natl Triolian Dobro mando
Victoria b-back Merrill alumnm b-back
Stradolin Vega banjolin
Sobell'dola Washburn b-back'dola
Eastmn: 615'dola 805 m'cello
Flatiron 3K OM