If you have a good number of long rides under your belt, including an Alps trip, you will be perfectly prepared to tackle the Dolomites. The Maratona dles Dolomites is one of the most majestic granfondos, and anyone partaking for the first time will, no doubt, be blown-away by the incredible mountain panoramas. Although the physical requirements for taking on the Maratona will not differ too much from an Alpine sportive, the mountains can feel a little bit more intimidating in the Dolomites. The mountains are packed closer together and have characteristically steep sides. You ride closer to the mountains faces here, closer to their peaks, you feel you are tip-toeing around a sleeping giant. On the day of the race, soak in the grandeur, enjoy the views but keep one eye on your speed or heart rate. Too often you can just be sucked along by a peloton, distracted by the views and end up going too fast, too soon. Consistency is king in endurance racing.
The Alps, by comparison, are a vast mountain range, with a more open feel. The climbs themselves are longer and more consistent in gradient. The Dolomites, force the roads to be less lengthy and have a few sharper kicks. Be prepared for some short bursts of powerful climbing to get over the steeper sections. Try some steeper hill repeats to acclimatise the legs in training and get used to being able to change your efforts and cadence to suit a changing gradient climb. Thankfully the roads of the Maratona are impeccable smooth, whereas the Alps generally suffer a rougher surface. So you can look forward to some really rewarding descending for your uphill efforts.
Otherwise, standard mountain sportive preparation applies. A compact chainset and a larger ratio cassette are advised. Make sure your fit position on the bike is correct, bike is in top condition mechanically, set your goal for the race and you have a corresponding training plan to stick to.
A final preparation point may be to find out as much as you can about the Maratona course before you ride it. Knowledge is power. Knowing where and how to apply your efforts or save your energy could be make all the difference.
Good luck and most of all enjoy!