There are a limited number of 240Ds around with 4-speed manuals.
Check out
MercedesShop - Mercedes Benz Parts and Technical Information
There are a couple of ecomodders who hang out there.
They have a diesel car forum and I believe there is a guy in there putting a M-B diesel in a Chevy pickup.
They have sources for M-B manual transmissions and parts.
I'm thinking hard about picking up a 84-85 300 CD (W123) and converting it to a more modern five speed. I may have to order the manual flywheel from Germany. Not sure yet. M-B automatics do not have locking torque converters. They last like the engine but feel slushy and kill FE. Mating the M-B four-banger to an American transmission will require custom machining.
Air bags are a necessity if you intend to put heavy loads in the truck. Air bag kits for S-10s are an off-the-shelf item.
Chevy axles can be had with ratios from 2.73 to 4.10.