Complex sentence: No.956 was first given a different variation of the standard arrangement, then brought into line with No.959, but by the end of 1922 both had been altered again, this time to the same mixed gear arrangement as 957/958.
Split into simpler sentences: No.956 was first given a different variation of the standard arrangement, then brought into line with No.959. By the end of 1922 both had been altered again, this time to the same arrangement as 957/958.