Having had to rescue a big boa in a mess last year, I completely understand what you are going through. Before we suddenly took that snake on we had no experience with bigger constrictors and it was a fast but very interesting learning curve. Best advice is be dead strict on your quarantine procedures and have the snake checked out by your vet. It's wonderful you decided to give this snake a second chance. Poor thing certainly deserves a lot better than what it was getting.