Drive a few miles sitting on the D shape and you will put the straight edge forward. Seriously Dave, I have no idea what is the 'correct way'. However, most furniture chairs are straight at the leading edge, rounded to the back. The 'D' shape cushions are B L O O D Y uncomfortable for any driving time.
The "D" cushions do not have any lift-the-dot tabs, nor do the kneeling cushions. The square seat cushions with the internal metal frame with springs below two layers of horse hair can also be found with an enclosed bottom with two side flaps that accept two female lift-the-dots per flap.
Notice the image of the MK-I or MK-I* carrier with the Vickers? Also note the MK-I* carriers have the locking tabs and lift-the-dot male portion on the support frame.
I have not looked for dates on the square cushion covers. Perhaps someone can check. The originals cannot be used for other than display, as they crack and turn to dust.
Consider getting the anodized lift-the-dots, not the plated ones. When you set them on the back rests, copy the originals for the lift off direction.
