how long have you been eating paleo? I am also a cyclist who has eaten this way for about 2 years. After having metabolic testing done I found out that I am able to burn all fat up until a heart rate of around 165, and then still use mostly (more than 50%) fat even into the 180s. This is something that develops over time, and I still consume carbs on long rides, but my reason for writing is to let you know that the traditional endurance athlete carb suggestions do not apply the same way on a low(ish) carb diet.

I have found coconut water works great, and for high intensity racing I'll use a Gu without any detrimental effects. Also, dates work amazingly well for a quick sugar fix and are super tasty.

Assuming your glycogen is topped off, you probably have roughly 200g of muscle glycogen in your legs that you could use for this, which is about 800 calories. Seems like you would easily deplete those stores in a 75 mile ride, so you'd want to be refueling with some glucose on the way.

Supposedly the glycogen loading technique to use beforehand is to deplete glycogen, then consume a high fat diet, which we do, followed by a high carb intake. It loads your glycogen stores far above what you would normally be able to top them off at. For carbs I'd eat white potatoes and/or rice. Alternately, you could just eat a fair amount of rice or potato in the morning of the ride to top off at your normal levels.

Edit: I've been thinking more about this, and unless you're out of the wind and parasitizing the paceline the whole time, you're going to be burning through your glycogen pretty rapidly. On a comfortable jaunt on the bike you could conceivably burn pretty much only lipids, but with something like this you're going to probably have pretty substantial stretches of carbohydrate use, even as a pretty well-trained individual. As such, I would take way more glucose in whatever form you decide on than you think you'll need.

Edit 2: I defer to Jeff and his experience.

Whats that? You mean you're not trying to increase your dead lift or squat? Endurance? How dare you! Just kidding. I would def read the Paleo Diet For Athletes. first 4 or 5 chapters. Lots of good science and co-authored by one of the best endurance coaches in the world. I would then also practice your eating on longer training rides and time trials. In terms of eating, i would do lots of sweet potatoes, bananas, and even white rice (in addition to lots of good quality fat and protein). I don't know how long a 75m race will take you. I do nordic ski racing, my longest race this year will be a 30k. It should take me between 1.5-1.75 hours. So I plan on having 1 gel within 5 minutes before start, then take in Heed about 6oz 30m in and then 6oz at the 1 hour mark. But I've practiced this before and its worked. On races under 45 minutes, i don't take in anything. Good luck. Oh and on my long training days or hikes over 3 hours I use banana chips, beef jerky and water!

I would definitely eat carbs while you're racing if you care about your performance. While in general it's good to avoid fructose, I would go for something that has a bit of fructose because there is some evidence that it can replenish your glycogen stores faster than glucose alone.

I don't know what exactly cyclists eat while riding, so I'm not sure whether my snack ideas are good suggestions or not, but you could try dried fruit, honey, sweet potato, or rice (which is pure glucose).