The exact firmware version isn't needed, mostly the 4.x.y version is enough, so 4.6.1 should be compatible with 4.6.3 as well. Even 4.5 could work, but need to try.
I doubt that the backup file really contains a list of the installed packages because they are not handled as "backupable" information. Next time you should create some opkg backup as well: HOW-TO: Script: List My OPKGs (to a file for backup)