Apple Mac 8600 - Manual (Page 113)

Take Apart Fan Assembly - 15
In addition, some of the original PM 8600 units shipped
without plastic air deflectors (p/n 922-3070). If you are
replacing the fan in one of these units, you must also order
an air deflector and install it before replacing the fan. That
is to say, the PM 8600 should have the air deflector and the
plastic baffle installed.
Refer to the Parts chapter for more information about the
parts themselves and to the “Baffle” and “Air Deflector”
take apart topics in this chapter for instructions on how to
install these parts.