To do that he's going to need more than to be a "tad more selective."
Gattis is a .260ish hitter who walks 5-6 percent of the time. He would have to improve one or both of those numbers quite substantially to be a .900 OPS player. 35 homers is also a bit of a stretch considering his 162 game average is 29 homers. I guess if he went to Texas or some other band box, an extra 5-6 homers over 162 games would be possible, but not likely.
Teams aren't going to view him as such either. They're going to value him as he is, not what he could be.
Games per homer isn't the best bet for Gattis since he pinch hit a lot his rookie season thus driving down the actual number of PA's per game. His homers per 600 ABs is 32. Only way I could see him reach that number though is for AL team so he could DH. But the man has legit power.