Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:6/8
K:G
['B3 BAG dB/c/d efg dB/c/d gdB', 'g3 gab']  
X:1
L:1/8
M:6/8
K:G
|: B3 BAG | dB/c/d efg | dB/c/d gdB | A3 DFA | B3 BAG | dB/c/d efg | dB/c/d gdB |1 cAF G2 A :|2 
 cAF GB/c/d |: g3 gab | e3 edB | g3 gab | bag a2 f | g3 gab | efe efg | dB/c/d gdB |1 
 cAF GB/c/d :|2 cAF G2 A ||  