If so, you dont want him with less range of motion. He could add another ~10 lbs, but he doesnt have the wide shoulders that would carry more than 10 lbs without making his arms and legs heavier than they need to be. If he adds weight, it needs to stay in his shoulders and hips. And he doesnt have the frame to make that more than nominal gains in those areas.

If he committed to becoming a post player, then he could add more weight, but you also run the risk of his appeal as a stretch 4/5 taking a hit.