How effective are the under dash AC duct outlets on a original car?

Been ruminating on how/where to put AC vents in/on my dash. Noticed that it seems like the typical format for most cars is two in the center of the dash and one at each corner. This puts them fairly high and you can get air from both sides.

I'm curious how the effectiveness of the under dash vent setup on original AC cars compares. Does it seem like it still cools the occupants as well, or well enough? Any loss having the vents lower under the dash rather than up high towards the top of the dash? How about not having a vent on both sides?

Thought about putting 2 vents in the middle of a junk Rallye dash where the radio would be, plus one in the corner next to the speedometer. But not sure where to put the one on the other end of the dash. And if the under dash vents work ok then I'd rather that option and keep it looking somewhat stock even if a '74 never came with a Rallye dash.

Thanks.