Round vents similar to the 164 ones shown above would be good for up/down and left/right air direction to both front seats. I know the draw of these is they are Volvo parts, but personally I think the 164 vents look a little too "aesthetically dated" with all that space between the four prongs - but maybe they look better cleaned up!?
I remember being in some Datsun model years ago that had orb-type dash vents. I don't have a wreckers nearby but it might be worth someone who regularly visits one glancing inside some late 1970s to early 80s cars. They might stumble on something "attractive" that would suit.
