Also Garth Davis from the Davis Clinic in Houston Texas is a vegan bariatric surgeon. He has a book called Proteinaholic that I've found very helpful and plan to use his advice post-op, when I have more freedom to eat my own way (more carbs because well.. vegetables)
I'm vegan and pre-op. I don't struggle at all to get 60-80g of Protein daily, so I wouldn't worry about that. That's my surgeon's recommendation, and while I haven't had my meeting with the dietician yet, I've heard that when she found out I was vegan she started researching vegan protein powders. There are a lot of good choices out there. So far, my favorites are the Orgain plant-based protein powders and the PlantFusion Cookies & Cream.
Edit: But, while protein is important, remember that other things are too (like fiber). And my friends post-op have suggested Beans will be super useful post-op, especially in the pureed stage.