The AF IMT 24 is an application for the position you're applying for though, so it would make sense that 11F would be the correct response. It's not asking for your current AFSC.
I always put 11XX (whatever the correct AFSC is). I also asked the POC in Oregon for clarification on this and he said it's also fine to just leave it blank - he just likes the form because it gives him a bunch of useful information about you, not because the version you send is going to be formally submitted. But that of course is probably at the discretion of whoever is handling the paperwork. Definitely don't put the wrong AFSC in there though, like 11M or something.