Details & Changes.

8 engine vent wings until ch.number 20-117901.
  Length 350mm.

9 engine vent wings from ch.number 20-117902.
Length 300mm.

Until ch.number 20-02817 there were no vent wings
to the cargo room.

From ch.number 20-02818 until 20-015399 the vent wings were 175mm long.

From ch.number 20-015400 until 20-117901 the
the vent wings were 350mm long.

And at last the later model from ch.number
20-117902 were 300mm long.