Carbonfibreboy has already mentioned the climbing factor. I have no idea what Mallorca is like, but his advice about have a lower gearing set-up is a good one. And be aware that there are likely to be faster, younger riders than you who love to chat as they up their pace, and while you try to keep up with them, you eventually have to drop off... and that can have significant issues later in the ride. yannigs made an excellent point about how corrosive that extra pacing can be.
All the other advance about intaking energy is very sound. Having a powder that dissolves in water is a good start, along with various energy bars, and making sure you intake as planned along the ride -- every 15 or 20 miles of the ride, for example. And adequate fluid intake is vital.
And as you are aware, datlas, I have trouble doing over 70km these days, but I do have a strong memory of doing many 200, 300, 400, 600, 1000 and 1200 events in previous years. Not up with the front-runners, but still within the specified time limits despite the prevailing weather and roads.