I personall gave up ... Support could not help me get this resolved. My main issue was not so much restoring the DB. Everything worked perfectly, until a few minutes after logging into SIM, the service account used wil get locked out in Active Directory, which was the account used to install 7.3.
Here is what I tried:
Backup and restored the db.
Created a new db, restored to the new db from the old 7.3.
Created a new db, and exported tables from the old 7.3 to the new 7.2 db.
I may have something else, and in all cases it would locked the service account. My DBA said, that the GUID may have changed for the new installation, which is why it kept locking out the account.
So before, dettaching the 7.3 db, I logged into SIM and since I could see my data, I took screenshots of the settings, credentials, discovery ... And started using the new db which the 7.2 installation created. Of course, all my data was gone at this point.
My advise, make note of your settings and start fresh ... I wasted 2 full days monkeying with this and nothing. I was up and running within 2 hours tops.