Somewhere in that SL site is a pic step by step description of a subframe swap,you don't even have to pull the engine.
Undo the four mounts,diconnect your brakes ,support the engine from above disconnect the engine mounts,'Disconnect the steering and check the steering box mounts while you're there and the installation is a reverse.
Use a used subframe from a W115 ( four cylinder car but NOT a diesel) and you may even locate one with "A" arm joints etc.Order a new mount bush kit and change the rubbers while you are there.I think you'll find that the joint broke as result of worn bushes on the "A" arms.
It's a weekends work for the DIY enthusiast ,a proper Merc shop can do it in 4 hours ,including alignment .The hold up is whether or not you used a new part or had an old part cleaned up and repainted etc.