For the 6500:
-OrangePC DOS Compatibility PCI card (620,530) somthing better than a 486 not necessarily an OrangePC but they seem to be the most available.
-SonnetTech TempoTrio (but who wouldn't want a USB/FW/ATA combo card).
-SonnetTech Crescendo/L2 G3 (" " " " " G3 in their Power Mac).
For the 6100:
-The material and the skills to do an atx conversion that will allow me to turn this into a sexy linux box.