72 Dart rear help. What do I have?

8.25 truck rear ends, maybe Dakotas? The giveaway is that the spring perches are on top of the housing (you've got them upside down in the pictures). Assuming that they're 5 bolt (Dakotas went to six lugs around '92-'93ish), they could be 5x4.5 or 5x5 depending on the year.
If you want to keep your 5x4 bolt circle, keep the 7.25 for now while you look for an 8.75. If you're converting to 5x4.5, they may be useable if they're not 5x5, and dependent on overall width. They'll need all the brackets cut off and new spring perches welded on.