trag, have you got a C-600 or were you making an observation from
everymac.com or the like?
I'm pretty tired, but it looks as if any of the clones with an oddball number of slots, and can be upgraded, seem to be lower end versions of a six slot capable MoBo. IIRC, each PCI Controller/Bridge IC handles a maximum of three slots so, for a workable hack, there'd have to be
a pair of PCI Controller/Bridge ICs.
Knowing a bit about Apple, there's just ONE PCI Controller/Bridge IC in the 6400/6360 and 6500 with a MAX of three PCI slots, which would include the COMM Slot II. The two slot riser works fine with a 6360 MoBo, but don't expect to add another slot with a three slot riser . . .
. . . unless of course, you steal the address of the CSII for the third slot. :
That's why I posted the links above:
PCI Bridge 3202
3 Slot 32 bit PCI Riser Card
Dimension : 155.00 mm * 65.88 mm * 1.60 mm
PCB Layer : 4
Interface : 32 bit / 5.0V
PCI to PCI Bridge IC : Intel® 21152 5
Insertion Direction : Left side
Device Setup : Software scan, manually setup
Golden Fingers : 5 ~ 8 u
EMI Prevention Design
Surge Protection Design
Of course, by "Software scan, manually setup," I'd probably have to assume it'll only work in a PC . . . :-/
. . . but just maybeeeee!!!!!!!!!!!!!!!!