There really isn't much new to tell about the 280SE Coupés and Convertibles apart from the different engine. This new engine replaced both the 250SE and the 300SE Coupés and Convertibles at the same time. The only way to tell a 280SE apart from these earlier models was to look at the badge on the boot.

With the introdcution of the 280SE 3,5 Coupé/Convertible models in 1969, Mercedes gave the existing 280SE Coupé/Convertible a small face-lift. The V8 engine gave Mercedes the chance to lower the grille and making it wider at the same time.
The wheelcovers and the design of the outside rearview mirror were modified slightly before the arrival of the new 'nose'. Certain small changes can also be found in the interior of the Coupés/Convertibles.

From the outside, the basis of the 280SE Coupé/Convertible was the 250SE Coupé/Convertible. So for a detailed description of the 280SE, please read chapter 5) 1965: The 250SE Coupés and Convertibles first. You can read the word "280SE" where it says "250SE". Below are things mentioned were the 280SE models differ from the 250SE models.

The wheelcovers were quite different from the 250SE and 300SE models which the 280SE replaced. Although these new wheelcovers look unchanged compared to those found of the 220SE and early 300SE models, they were in fact now made out of one piece instead of a seperate rim and hubcap. Seen from the side, you can also notice that the new wheelcovers are 'thinner-looking' than the older ones. These 'one-piece' wheelcovers can also be found on other contemporary Mercedes-benz models.

As said above, the design of the grille changed in 1969, it became lower and wider. When you put the two cars next to each other, you can clearly see the difference. Cars with the newer and lower grille were called "Flachkuhler" models ('flach' meaning flat), previous cars were now called "Hochkuhler" ('hoch' meaning high, 'kuhler' meaning radiator grille).
The rubber inserts on the front and rear bumper were also part of the face-lift and can also be found on the W108 and W109 sedan models from 1965. According to some these rubber inserts were long overdue because they reduced the chance of denting the bumpers while parking the car.

A smaller change with the arrival of the 280SE Coupé/Convertible models was the design of the outside rearview mirror. From the more round looking older mirror to one that was more squared looking. This new rearview mirror, together with the new wheelcovers, can also be found on other contemporary Mercedes-benz models.

Below are things mentioned where the 280SE Coupé/Convertible models differ from the 250SE Coupé/Convertible models so for a more detailed description of the interior of a 280SE, please read chapter 5) 1965: The 250SE Coupé and Convertible first. You can read the word "280SE" where it says "250SE".

A significant change for the dashboard was that the use of precious wood was reduced. Before the 280 SE Coupé/Convertible models, the instruments were set in wood, now they were covered by leather in the same colour as the rest of the dashboard. The horn ring seems also to have changed slightly at the same time.

Similar to the sedan models (read chapter 7) 1965: The Second Generation: 200, 200D, 230 and 230S) some interior handles were changed in design, the door-opener (no. 1) was given a more squared appearance. The switch to lock the door (no. 2) was also given a more 'squared' appearance.