Note: You not welding them because when you stretch the frame, it may "move" their location.

With the frame laid down, and one of the drawer members under it to support the spacers, place the spacers on each side.

The end of them is to be 7 1/32" away from the upper cross member. Look at the diagram.

Insure they are parallel and flush with the U-channel and C-clamp in two places for each.

Tack them on this side in 3 spots.

You may need to grind this off later, so make sure the tacks aren't longer than 1/4" or so.

Flip over the frame and tack the other side.