i think aslong as the speedo/odometer matches so digi or analoge
you can swap the ecu and key easily
im not sure the ring matters but if you like...
if it were me i'd get an ecu and key swap the ecu and use take a door lock out to have another key made from the locks code and use the new ecu's key as a fob/keyring just to work the immobiliser

its easy to have a key cut from any lock but its the coding that costs and sucks