Does anyone sell pre-cut parts for frame?

[Gero]

The will be a new stock frame, discussed here. Go ahead and build the final frame.

New Stock Frame Design

You could take the 2x4 frame piece (that the plywood attaches to) and notch it out. I have done this in the past by setting the fence up the distance I need to take out. Move the board past the cut and raise the saw until it plunges through. Then push the board to the other cut line. Then I use a jig saw to cut to my line.

Edit: 872 posts might be a little to much to go through. Perhaps work you way bottom up
Edit2: There is also a nice minimalistic approach here: 80 Dollar, 60 minute Frame Build aka 80/60 - #13 by Bee