First order of business is to be able to seat in it. Springs on the driver's seat had collapsed, but luckily I still have one of the seats from the 450SEL 6.9.
First, we remove the front seat. Four 10mm bolts on all four corners of the tracks, and a 10mm bolted to the transmission tunnel track.
Close enough! Still, I will buy a correct upholstery kit or good used covers in the near future. Notice the awful wear on the driver's seat back and armrest!
Pool noodles are your friends. Mercedes-Benz sells a similar product for an astronomical price, neatly packaged and with the MB logo. I'll save my money to put into other parts! Two full pool noodles will be enough for one seat.
Tried and tested several times until I found a good comfort level somewhere in between a collapsed mess and a church pew.