Feeding schedules (either once a day or twice a day or thrice a day or whatever schedule) is dependent on the dog. Some dogs can gorge on big meals without problems while other dogs can't. Some dogs can digest their food faster while others can't. Feeding kibble poses a bit of a challenge when gorging as it expands in the stomach and the amount of carbs it contains can overload the pancreas and it takes a long while to digest. Whereas feeding wet food or home-prepared meals can digest and metabolize much quicker.
In any case, what you want is for the dog to eat until he is full to put his digestive system up to fully function as it was designed to do then have time to digest all his food and have a period of digestive rest before he eats again.
That said, how often to feed your dog is first and foremost decided by your dog and what you feed him. Then whatever he does okay with, you can tailor with your own convenience - if your dog is fine eating X times a day, then you get to choose how often you feed him at your convenience.
Some signs that the frequency of feeding is a problem for the dog:
1.) Skipping meals - reduce frequency
2.) Diarrhea - increase frequency to make individual meals smaller
In any case, the amount of food a dog needs per day is dictated by his condition - too fat - reduce the amount, too skinny - increase the amount. It doesn't have any relationship with how often you feed your dog.
As far as transitioning from 3x a day to twice a day, I would simply take the total serving for the day and divide by 2 and start him off on the bigger meal the very next day and see how he does.
Thanks for your response and for your advice! We'll probably make the switch this coming weekend and see how it goes!