Chrysler 300 & 300L

Hi guys,
I MIGHT get the opportunity to rummage through 3 Chrysler 300's before they go off to the crusher. One is a 1970 300, and the other two are 1965 300L's. They are totally rotted to hell, but still have the original diffy's in them. My question is (are) are these 8-3/4 rears? If so, how can I tell without removing the center chuck, if they're Sure Grip rears? Will the center sections fit into the 8-3/4 housing that is in my 69 Dart Swinger 340?
I believe the '70 has a 440, but are the 300L's 383's or 413's?
If I can only pull ONE engine/trans out, which one should I keep for a future Dart project?

Thanks for helping me out.

George