If you can mount the disks from your dead G4 Tower I'm pretty sure you should in principle just be able to drag the System directory over from there onto your Pismo's boot disk and be good to go. (When you say "can't boot from it", do you mean over FireWire?) There's no conflict between an OS 9 system folder and OS X, so there shouldn't be any risk in dragging the folder over and trying it.
Only a single slot.
(Which is why I was initially surprised to learn that the Airport slot wasn't hanging off the second slot of a "normal" dual-slot CardBus bridge IC. As noted, looking up the datasheet for the CardBus bridge confirmed that it only supports one slot. I suppose Apple's justification for grafting the weird subset-of-PCMCIA onto the Keylargo "Southbridge" was to avoid having to include a dedicated PCMCIA/CardBus bridge IC in any desktop machines using AirPort. It makes sense in a twisted way.)