i would not put a a 44 in there. thats about the same strength of the fj40 axle.
I was suggesting a 44 for cost and for a centered differential. I'd even suggest a 12 bolt or a 10 bolt - after all, they work fine in 1/2 pickups - but a 44, if you get a Scout one (or a JK one for that matter), is the same width as the '40. Also, the other reason behind the suggestion is exactly what you pointed out - it's the same strength as the one he hasn't broken.
What kind of mileage can you get with a 5.3 LS motor?
12 - 14 mpg. with a 6.0 you should get 14-16