I did a lot of research and finally bought a stripped lower to begin the SBR build. Based on my research, you need to fill out the From 1 and it MUST be two sided and have two copies sent in. I did mine through a trust so it was easier to complete. Based on what I have read, you can only apply for one configuration i.e .223 in 10.5" barrel. It used to be acceptable, based on what I read, to insert multiple calibers and multiple barrel lengths. Once I get my paperwork back I am good to go for the one configuration. It says that you shall notify them if you change the configuration, I am guessing that a certified letter telling them I went to an 11.5" 9mm upper will make that legal as well.
To be on the safe side I will probably trade uppers so I do not possess multiple SB uppers. Probably overkill to do it that way, but not worth finding out the hard way I was wrong. I will be getting the lower engraved to check that box as well. I will post pictures in 9 or 10 months when the stamp comes in and it is done;-)