Hence why I said "CAN reach 10 feet", not WILL, and stated full grown length as 16-20'. I am not saying in any way shape or form that this snake will be that big, simply that it can be, and anyone who plans to keep them needs to keep their size in mind. Facts remain that most people do not know how to/cannot care for snakes of this size. I keep Burms, too, for the record.
Yes, it does sound like this animal has had a terrible diet throughout it's life. I'd start out a bit on the light side when you begin feeding just to ease the snake into a regular, healthy feeding schedule. (: