Hm.. with a large BCI, I would recommend two people handling it, at least until you get used-to the way the snake moves. I regularly handle a large female, owned by my friend. This is the most laid-back snake I have seen, but at times she can do unexpected things. She is known to wrap her tail tightly around the leg or arm of someone holding her; especially if they are nervous and moving around a lot! I think she does it, more out of fear of falling; tryin to get a good grip. But I brought it up because, sometimes it is necessary to have a friend or helper, remove that tail from your leg!
They are also apt to make sudden head motions upward. This could result in the snake hooking its head around something (like, say, a coat hanger.) This, you do not want; it is dangerous. You have to keep track of that head at all times!!
I would get used-to handling the boa, for awhile, since yer friend does not plan on selling it. Also, try to get to a pet store or other place where they have alrge boas, and will elt you handle one. It is a much different experience than handling a smaller BP!