An IEP is for kids that usually end up on the Special Ed tract through school. It's to supply them with assistance that is specific to that end. That they'll do as well as possible but will likely have to have assistance through the special ed program. It can still be extremely helpful to use this plan even if your son's disability isn't that bad. It will legally give him more options and the school will have to find the money to pay for things he gets.
A 504 plan is specifically planned for kids who just don't quite fit in, have health problems, need an aid sometime to help them with managing stuff like behaviors or one on one time, and help him with classwork.
Our grandson had a 504 plan at his last school and he, along with a couple of other boys, and she helped them when they had table time to do school work and she managed them in the hallway when they needed time out of the classroom.
The school he goes to now refuses to do a plan with him, he doesn't have any acting out in class. I informed them that he took meds and had an ADHD diagnosis and they were required to have a 504 plan just for that reason alone. They wouldn't have one for him. So he changed schools this year. He has a good 504 plan in place already.
The teachers need to research their resources and find what they can do. They have psychologists and therapist and assistants at their disposal. Please ask the teacher to work on this on her own. She/he has what they need to help your son the best.