Ask the members here https://www.benzworld.org/forums/w164-m-class/

 

I've read somewhere that 300 to 350# tongue weight is preferred MAX for ML.

 

That engine is more than capable of whatever the chassis is able to tow. Max tow weight is rated at 3500 kg (7700 lbs) WITH trailer brakes and a quality brake controller. The W164 CDi is quite heavy with a gross weight (with fuel and passengers/cargo) of 6200lbs, and only 400lbs lighter than its bigger cousin, the GL. so really, in order to tow safely, the only thing you need to get under control is tongue weight and sway. With a decent weight equalizer system and sway bar(s), i Don't doubt the ML CDI could easily and comfortably tow just shy of 8k lbs.

 

I'd guess ML chassis is similarly constructed to sprinter but not sure... ML is 4matic so there's that especially helpful when hauling out on a algae-covered boatramp @lowtide.