I'm using a cbm 286 bridgeboard to activate the isa slots of my 4000T with an NE2000 without problems...
You can use your 3com too if you find a cbm bridgeboard... a 286 or 386 would be a good idea, 8086 ones use 8 bit isas and you may have problems, I don't know...
download etherbridge.lha from Aminet.