I'd say there's a good chance it's square. You should probably file the paint off the faces, at least.

You can probably get an idea how straight they are by colouring over the ends with a permanent marker, half-tightening the cups and then undoing them again to see where they've rubbed off the ink...

And if you take the bare frame into a shop, they shouldn't charge you much to face the BB of an ally frame.