I have a 14month old female maremma. I'm no expert on this breed yet but I wanted to chime in + say that when I got my girl as an 8 week old pup, I was surprised by how standoffish she was. I'm used to exuberant little heelers and kelpies, and it took a while to get used to my gentle spirited, shy little maremma. I learnt quickly that I needed to let her come to me to be affectionate. She is really sweet with me now but it took a while. And I guess that will go double for your boy since he has had such a bad start.
Also, re guarding stock, I've been training my girl around our livestock since she was about 12 weeks. Now at 14 months she is pretty good but as adolescence has hit, still occasionally wants to play. So she STILL needs correction and supervision, and I don't believe she will be totally trustworthy until somewhere between 18 months and 2 years. So take it slow with your boy and don't expect him to properly 'work' for quite some time.
I hope it's been going well with the new pup if she is now with you. They are so ridiculously lovable! (and sometimes just ridiculously ridiculous)