The head gasket design was changed in the mid 70's so that now the 230sl and the m129e 250se-sl motors all use the same head gasket.
I ordered mine from Metric Motors when I ordered the piston ring sets. it was $92.00 (shipping included)
The MBZ dealer "blue box" part# 129 016 15 20 appears to be the head gasket only, I didn't see a full gasket set listed in the EPC online catalog.
Al
66 230sl
113-042-10-014715
904/396 blue, Ivory Tex
condition: not-as-rusty-as-before-bucket