Apple Performa 6400/180 - Manual (Page 32)

Basics Expansion Bay - 30
Chassis Revision Identification
There are two versions of the Metal Chassis Assembly for
the Power Macintosh/Performa 6400 and 6500 series
machines. Part number 922-2272 Chassis, Metal, Rev. A
should be used for all Power Macintosh/Performa 6400
series machines with the exception of the PM/Perf 6400/
200 with Zip Drive. Part number 922-2707 Chassis,
Metal, Rev. B should be used for all Power Macintosh 6500
series machine as well as the PM/Perf 6400/200 with Zip
Drive.