How to Add the External Projections
Open the 1-D spectra to add. In the case of a homo-nuclear correlation 2-D experiment, a single spectrum is enough for both projections.
Return to the main plot and choose Format > Overlay.
You will see the list of the other windows. Check the box at the left of the projections.
Adjust the amplification factors (they are reported into the last column, “amplif.”). You can press Fit for an automatic amplification.
If you enter a numerical value, click Apply or press Return to update the plot.
Close the dialog.
The projections fill the empty borders (where there's no frequency scale). To move them to a different border, it's enough to move the scales. Choose Format > Axes & Scales, click Units, etc...
When the dialog is closed, you can still change the relative amplification of a projection with the mouse wheel (move the mouse over the projection to amplify). If you have no scroll wheel, use the keys * and /. The latter shortcuts, however, only work with the last projection of each document.
You can drag the four borders with the mouse to leave more or less space, around it, for the projections.
You can insert an empty space between the main plot and the projection: open the iNMR preferences, reach the second panel (Display) and set the parameter called “Gap under the Projections”.