Last weekend I did a ~1% 300k in 11:45 riding time, fuelled with 720g of sugar and a bit of sodium citrate. Split it into 4 baggies and had 180g in a bottle every 75km. I also had some cola and crisps at each stop, except the last one, I had bread and fruit. Since I was slower than you planned, I only did 6,734 kJ. I plan to up the sugar from 60g an hour to 80g an hour for my next long ride so I can keep my power a bit higher, and it’s easier/cheaper than fussing around with gels or junk food.
Carbs are more like 4 cals per gram. You brain farted the fat calories per gram. 
Yep. You’re right. Had the calories in a gram of fat on the brain. Advice remains the same.
Ask the tour group now what they will have / what will be on course and start using that now so your stomach is used to it.
At least for me, there is stuff I’ve had on rides that just doesn’t agree with me at all - e.g., Gu, precision hydration.
For a ride like this it would suck to get derailed because the available calorie options weren’t palatable or messed up your GI
Good luck and post pics
I did 202 miles last year in just over 10 hours - 48yo and 3.3w/kg. As others have said, you want to focus on consuming as many carbs as you can comfortably digest. It used to be recommended to target 60-90 carbs, but now you see seasoned athletes going well higher. Try a longer ride with 75-80 g/hr and see how it goes. Add more if you can comfortably do so. Other factors to consider are taste (palette fatigue), type and cost. Personally, I’m fine with endless gels, but others grow tired of them. Some prefer drink mix, but that doesn’t work well for me on hotter races when I want to drink to thirst. Nevertheless, I have used drink mix successfully as primary fuel source on some long rides.
The secondary consideration for me is hydration as I am a somewhat heavy and salty sweater. So, trying to get enough sodium for me is important. Everyone is different in this regard.
If you can confirm what will be on course (Enervit, SIS, or whatever), you could start training with those products. I always try to plan to have all my own food if possible as I like to train for weeks with my race fuel. I am not sure if you can pickup your own supplies at the stops. If so, you can use anything. Otherwise, you may be relying on the supplies available on course.
Don’t go crazy at that big breakfast. I keep it light on race day. Have fun and, most importantly, take and share some pics.
Unless you have tried Enervit or SIS before, I’d suggest you take gels and powders that you know you’re happy with. I’ve seen many people comment on taking an untried energy drink and found it too sweet. They ended up drinking water only. Pack this in ziploc bags for each bottle and fill each time you get water somewhere.
Whole foods like fruit, a sandwich, a coke should be okay to get at roadside cafes or shops.
Eat from the start, as you’ll be depleting your reserves quicker than you can replenish them, so the deficit increases for every hour. Make sure you’re fully topped up the day before, so you start on a full tank (glycogen stores).
Check the weather and see if the wind. If you know it’s going to be a head wind all day, and it happens to turn, then your mind is easier to accept that thinking it’s going to be a tailwind. Prevailing winds in that region are known as Scirocco (SE) and Mistral (Northerly) are the two main ones.