Do this:
1. Backup Flash on 3600 controller. Save the file somewhere.
2. Move/Migrate License(s) from 3600 to the 7220 using the licensing site. (save the keys that are generated somewhere)
3. Get the 7200 up on the network with the version of code you want.
4. Copy the flashbackup.tar.gz file to the 7220.
5. Execute Restore Flash (do not reboot)
6. Paste in the new licenses
7. Get a console cable and plug it into the 7220
8. Reboot the controller and DO NOT SAVE the CONFIGURATION (if you save config, you will remove everything).
9. After the controller reboots, reconfigure your interfaces on your 7220 using the console.