Roadster vs GT Doors

Easy to see the difference on these pictures of stripped doors from joshuabart.plus.com

Different waist-rail end pieces, the GT outer seal sitting up on its trim strip on top of the door, and the GT triangular finisher above the latch.

Both quarter-lights sit on top of the door, but the GT has the bright trim strip carrying the outer seal covering the bottom rail of the GT frame:

The trim-strip projects above the top of the door by about an inch because with the higher roof-line of the GT the drop-glasses are taller, and the roadster glass is already at the bottom of the door when fully open, which would leave the GT glass sticking up. In later years they probably wouldn't have been allowed to spend the money on a unique bit of trim.