I guideline I use for the entire IM. It has worked for me. I also use Accel gels, 12 in a bottle with some water to make them fluid.
These numbers work for me.
You need to replace 30% of what you use.
What you will use: 5 cal per pound per hour.
My IMCDA race:
270 lbs x 5 cal x 13.5 hours = 18225 cals x .3 = 5467 cals
easier to take cals on the bike
125 lbs x 5 cal x 12 hours = 7500 cals x .3 = 2250 cals for the race with a 12 hour time (guess)
maybe try to get 225/ hour on the bike.
I did do a lot of testing on long bikes and mutliple long bricks (140k-20k). The long bricks were for mental training and nutrition and did there job, but I was really careful to not get hurt. With the nutrition down and good training it I was able to cut my time by 2.5 hours, so the brick work was worth it.