Thing with Ironman is that after the swim you have to ride a bike and after the bike ride you then have to run a full marathon. It’s quite easy to do 112 mile bike ride on a reasonable amount of half-arsed eating and be able to finish it ok. The trouble here is that you really need to finish the bike ride ready to go and run 26.2 miles…
I would plan on aiming for 80g of carbs per hour. That is like 2 bars or 4 gels.
Practice this beforehand as it’s a lot for your stomach to get used to…