Your pretty lucky to have the build sheet and the buck tag.
The Sched. Build Date code
(04K) is what goes on your door data plate.
The buck tag date is the date the car was bucked for assembly scheduling I believe. My car had a scheduled build date code 15B (Feb 15, 1967) on the door data plate. My buck tag says B22, and according to Kevin Marti, it was actually built on Feb 23rd.
I would say the DSO for your car is Atlanta (21). DSO stands for District Sales Office and I believe the Region District would be the same thing.
I'm not sure on the engine code. It would seem to be about right though. I'm not sure if the cast in codes are date codes. Are you talking about a casting code on your engine or a stamped code?
I think the differnce between deluxe and standard belts is a push button or a lift latch and also chrome trim around the latch. These people did a great job with mine maybe twelve years ago. They will restore belts you send them or will sell you restored seat belts. They know what belts to sell you and you will get the correct retractors too. My car had no belts when I bought it. I sent them some belts I found in a junk yard for about $15 from a coupe as a core and they sent me the restored belts with correct convertible non-retractors.
Ssnake Oyl Products