Hi Stephen, apologies if this a little late, just saw your posting. I had two broken pillars on my '68 S2 when I bought her (See pics). I first removed the interior glued vinyl, sanded and buffed off the remaining glue and old dusty FG, I use carbon fibre cut into "L" shaped pieces and layered over "one, then two" 5 times. I kept the height and the tension using a bucket of sand and an adjustable strap around the body. I used one of those flexible applicators between the door and pillar to ensure the angle was correct too. finished off the surface with Bondo FG Resin Jelly, it sticks and sets hard, trimmed the FG and Jelly with my Dremel, both have come out strong and aligned, took the paint well too.
Hope it helps,
Cheers, Keith