Hi DmcL,
I'm 98 percent sure there's no way the vents can come through the front of either the gauge cluster or the passenger side dash trim piece, they have to be popped out of the pivot pin holes and slid out the rear, pretty easy, once the gauge cluster and passenger trim piece are out of the car.
And just for extra info, once the vents are out you can disassemble them further for easier cleaning or replacing any pieces that may have broke over the years. Mine weren't broken, but half of mine were 'upside down' and annoying to look at since they didn't match the other vents.

It is kind of tricky getting all the slats lined back up properly into the vent housing when you reassemble, I usually balance all the slats vertically on the sliding piece and slowly slide the vent housing over them until I can rotate the whole unit horizontally so the slats can't fall out, then click the other housing half back on.
Hard to explain, but if you do eventually take your vents apart, you'll see how frustrating it is when the slats keep falling apart like puzzle pieces lol.

84 SS metallic blue 350/350th
87 SS T-tops 383 stroker t5 5 speed (sold)
85 SS hardtop needs motor (sold)