Further seat info. The Mercedes seats are too wide in the shoulder area for the convertible top mechanism on a GTC. I have now swapped in some seats from a Mazda Miata, They fit well.
The original factory headlights are still installed on my 81 GTC however the shells are rotted and unusable. They are CIBIE "Super Bi-Iodo" headlights with the horse logo in the center of the lens, which according to the markings on the light were manufactured in Brazil