Seems like a deal, I think

Well, the B body rear end will not fit the A body due to width. The center section is probably not a suregrip equiped rear and not really worth the expense up upgrading it to one since you can get one new, all new for a reasonable price.
$120 for a 8-3/4 center is ethier a know nothing guy giving it away or it's an open rear. Know for sure that it's a sure grip before you get it.