AST/Orange PC cards for System 6:

The AST 286 and Orange versions should work fine in a System 6 Mac II. They are very limited, but that is a challenge in itself.

The Orange NuBus 386 card -- perhaps not all versions -- is the one with an ISA slot which I used for my experiments here: http://www.vintagemacworld.com/O386.html I didn't get it working well with System 6, but others may be more successful.