While it is correct that the user's guide states the requirement of a 386 or higher CPU, this is a misprint. It is important to note that the driver will not install on anything less than a 486, and that all pre-sales and specification materials other than this one page indicate that a 486 or higher CPU is required for use with the LaserWriter 8500.
You can still use the printer by using the built-in driver that comes with the version of Windows installed. Simply choose an alternate printer description file such as the LaserWriter 12/640 or simply "LaserWriter" to print to the 8500. You will not get the full benefit of using the Apple-supplied driver but you will most likely be able to print to the LaserWriter 8500.