I'm getting a little out of my area of knowledge here so hopefully someone will double check me. But...

To me those do indeed look like the same series of terminals. If I recall right the difference in that the 59 series is slightly wider than the 56. I think what you are looking at is just two different production designs. If you compare most of your underdash stuff, with the terminal size on a sealed beam headlight and its wiring you should see it.

For specificity sake, when you look up replacements in a catalog both the male and female ends you show there are "terminals" the plastic housings they go in that insulate the bare terminals to prevent shorting, have one or multiple positions, and may or may not have a locking clip, are called connectors. Again in catalogs, I know what you meant though.

EDIT- HEY! I got it right! Here you go.
Packard 56, 58, and 59 series
Never seen a 58 anywhere on a car myself.