Hopefully someone can grab this complete 5 speed conversion kit. Looks like it includes the linkage, 5 speed, crossmember, driveshaft, slave cylinder, flywheel. It's at $1 with 4 days left. It's some sort of shop selling this.
http://cgi.ebay.de/Mercedes-Benz-W123-5-Gang-Getriebe-zum-Nachruesten-TOP_W0QQitemZ280392476140QQcmdZViewItemQQptZAutoteile_Zubeh%C3%B6r?hash=item4148b1a5ec&_trksid=p3286.c0.m14