The LaserWriter 8500 requires a parallel cable with a 1284C connector on the end that attaches to the printer. A 25-pin parallel connector would only fit on the SCSI port of the printer, which will force the printer to enter the paper out - paper jam error state when started with this cable attached.
The parallel cable used to connect a PC to the LaserWriter 8500 must be IEEE 1284 compliant. Since IEEE 1284 has become a standard interface for parallel PC connectivity, many third-party vendors offer cables with this specification.
This cable should also be available from your Apple Dealer as part number M4235ZM/A.