GX Printer Drivers are not supported in Mac OS 8. The last version of Mac OS that supports GX Printer Drivers is Mac OS 7.6.1.
Details from the Mac OS 8 Read Me "About QuickDraw GX":
Mac OS Unified Printing Architecture; GX Printer Drivers and GX Printing Extensions No Longer Supported.
Beginning with Mac OS 8 and QuickDraw GX 1.1.6, Apple will provide a unified operating system printing architecture, standardizing on classic (non-GX) QuickDraw printing and printer drivers. With the unified printing architecture, QuickDraw GX printer drivers and QuickDraw GX printing extensions will not be supported in Mac OS 8 and future Mac OS releases.
Other than simplifying the printing procedure, the impact of Apple's new unified printing architecture will be fairly minimal. For applications that work in both QuickDraw GX and classic QuickDraw printing environments, no changes in operation will be necessary.
Customers wanting to print from their QuickDraw GX-only application will have to obtain a version of the application upgraded to be able to print via non-QuickDraw GX printing.