Measure the dimensions of the duct opening only. Make sure you have about one inch on all four sides of the hole for the lip to rest on. If that is problematic then please call us for advice.
True. Cold air returns have rectangular shaped openings measuring about 3/4 by 1 3/4 inches. This is typical dimensioning for vintage homes. Heat registers have openings that are roughly square shaped.
Quick answer...yes. However, only in a cold air return. Yes, I suppose we could do it in the register style with the squares instead of rectangles, but we are talking quite a bit more money since the jigs are not set up for squares.
No...you'll have to do that yourself. Experiment on the back first.
Probably. Call us and we'll talk.
Probably not. That is likely to affect the joinery...and not in a good way.
Eggcrates are sturdier.
Sure, why not. But the standard wood (oak) may have too coarse a grain structure to look good with paint on it. You'll probably want to use a grain filler first, or even easier just get them in maple (which has a tight grain structure). It is best to remove dampers with a screwdriver first so you don't get paint on them. It's easy.