Migrating system and user databases to a new server by moving the LUN
You will not be able to detatch system databases. If they are not open to properly migrating the server level objects to another server, then I would opt for restoring system databases over trying to replace them. Ensure you are on the same, exact build number or master will not restore. You will also likely have to update the server name in master, if your new server does not have the same hostname.

I would also insiste on a backup of every user databae before that LUN is moved anywhere. (Just in case.)