741, 742 and 489 are the last three casting numbers of the commonly used center sections, there are other numbers too.
741 is the "weakest".
Stock, 742 is arguably the strongest.
489 uses a crush sleeve that can collapse under high HP applications causing catastrophic failure. An inexpensive shim and spacer kit fixes that and makes it top dog of the three.
I know the gear carrier interchanges between them, but that's about it, for the center section anyway. As for the casting numbers referring to what body they are in, not really, it's more of an application thing. /6 car, likely to have a 741. Big block automatic, 745/489. But even that is dependent. My 64 300 stick car had a 742, later BB stick cars usually got a Dana.