Joe you could restrict the air some but keep in mind as mentioned it is designed to heat the basement in cold weather. We seldom use the furnace but when we do it heats really fast. We only have one furnace but it's a good one.
I'll have to take a look in the morning but I believe my basement vents have a cover in them. I do have a cutout like you show in the picture Joe but it's a dead end. It's not cut all the way through. That's what I thought you were showing.
Phil it looks like just the bottom of what could be the channel / duct is drilled. I do have a scope that I should send in there to see what it does from there.