How does vinyl replacement window sit in frame?

Translated: "I don't have a clue so I will ask you rhetorical questions instead"

Keith, there's no need to post the same question twice, under different subject lines, on the same day, six minutes apart. It doesn't improve your chances of getting a response at all.

Too many possible frame types/profiles to answer here on your specific windows.

Did you ask them where you bought the windows ?

AMUN

...When I removed the original window, I had nothing left except the 2x4 studs that make up the frame. Then of course, you have a half inch of plywood, and the siding.

The original window butted right up againt the aluminum siding. So when I removed the original window, I needed to do something with the siding, like put a j-channel all around the perimeter.

If I have the window sit entirely on the frame stud, then the sill of the new window, with it's drain holes, hangs over the plywood -not good.

Keith

You might not have bought the right window.

The frames come in many profiles and depths. Is the new frame as "thick" (inside to outside) as the old one ?

But you have to get it out farther, so water is not going behind the sheathing/siding. Or make up a vinyl or aluminum sill extension. Then you may have to build up the frame inside, level with the plaster/drywall

Check again where you bought it, they are the ones who are going to know.

AMUN

Translated: "I don't have a clue how to help you, but I just have to say something"