Finally, go over their complete other story for the solar system model (6)
I believe the answer is:
orrery
'the solar system model' is the definition.
(I've seen this in another clue)
'finally go over their complete other story' is the wordplay.
'finally' suggests the final letters.
The final letters of 'go over their complete other story' are 'ORRERY'.
'for' acts as a link.
(Other definitions for orrery that I've seen before include "Clockwork model of the sun and planets" , "Err, Roy, on the side of a model of the solar system" , "Clockwork model of the solar system" , "Mechanical model of the solar system" , "Planetary model" .)