After the model was made I started in on mortising of the long muntins. All of the mortises are punched at an angle so the layout took a bit of head scratching, but in the end it all came together just like the drawing. Thank God they turned out parallel!
Also, you should know that the interior is stain-grade so I had to take a lot of time making sure the coping on the interior side looks extra good.
Finished muntin, interior
The next step will be to fit the smaller muntins.