The AMT 61 Lincoln is a 4 door hardtop, I added the B pillar to make it a sedan. Why? Simply to make it more correct to what was normally found at a dealer.

The 61 Lincoln hardtop was a planned model but was cancelled early in production after only a few units were built. Some of those were converted to pillared sedans. It is not known if any of the remaining were sold to the public. The linked Curbside Classics story goes into more detail.

Once I decided to add the B pillar, I noticed from pictures of the real car that it was very close to vertical which I found unusual. Maybe it was that way for the best function of the suicide doors, or maybe the stylist simply thought it looked better. To get it consistent, I made a template by tracing the front window outline of my unbuilt 67 Lincoln onto 0.020 inch sheet plastic as they looked the same to me.