Hi Karl,
Quickest way is to over-write the radio with an existing codeplug that matches. Try saving the codeplug from one of your 'old' 340's and write it directly over the top of the new radios. Depending on the codeplug/firmware version this might work. Just make sure you disable the password in the CPS.
Try this and let us know how you get on. If this fails you will need to flash the radio to the latest firmware (and require the latest CPS version) in order to overwrite the radios. The other alternative is to 'find' the password in the RAM of the radio (i still after all these years don't know how to do that... So if anyone reading this does please feel free to post the answer

).
BW