I haven't eaten meat or fish for decades, and I know that does not have to be an insurmountable obstacle to building mass and holding on to it. I'm about 70 pounds heavier than when I started a non-meat diet, and most of that is additional lean mass added over time.
Currently, my protein intake is pretty close to the .8g/lb range you are considering, although for significant periods I ranged between 1.5-2 g/lb, relying primarily on eggwhites, cottage cheese and sometimes whey, with small contributions from other sources.
Anyway, if you try going meatless for a while, it may limit your options when eating out, but it does not have to mean abandoning body composition goals.