I can't get past the ProMaster's rear axle - every time I see one I want to flip the axle to actually have some clearance - as it is I think it would get hung up too easily. Sure the clearance might be similar to the diff housing of some axles - but its all the way across... That might be a product you could offer!
Here is an image of the ProMaster's front suspension I found a while ago - I was thinking if you pulled out the sprinter's transverse leaf and added your spacer you might be able to fit the ML diff in the space provided - then use the ProMaster's hub assembly with the regular sprinter lower A arms and the ProMasters strut / spring assembly.
You'd have to come up with a way to connect the ProMaster hub to the Mercedes diff - What kind of CVs are used on the diff? Are they the 6 bolt "Lobro" type as used on VW/Porsche/BMW? That would make it easier...
We are planning on making some parts for Promasters in the very near future. Right now we are just trying to focus on getting all our products done for the Sprinter platforms.
The ML diff does not have the 6 bolt type CVs similar to a VW. They are the press in style, similar to a later model Tacoma or Tundra. They just pop in / out. I'll try to snap a more detailed photo of them this week.
Been waiting for a couple steering universals and some steering shaft material to wrap up the front end. So in the meanwhile, we've spent the past couple days chipping away at the prototype rear bumper. Few more details to wrap up and she will be off to powder coat!
-Rob