Hi Mike,
Welcome from another truck guy...
Here's a short translation from MB into "truck" Diesel:
OM617: 5 cyl, 3l, iron head. Non-crossflow iron head. Legendary reliability but tough to get a lot of power out of due to limitations of flow and fuel. Has an inline M or MW pump.
OM603: 6 cyl 3/3.5l, Aluminum crossflow head. More modern design but watch out for 3.5l engines known to bend rods. Also watch out for early aluminum heads which can crack if overheated. Has an inline M pump with 5.5mm elements. Design is similar to a 12 valve Cummins. Easier to build more power with this one.
OM606 Turbo: '98/'99 E300. Evolutionary design similar to OM603. Has a 24 valve head. Much like a 24 valve Cummins but pump is still inline with 7mm elements and is electronically controlled. Elements are compatible with M pumps. This engine has the most power potential.
As for performance parts, it's pretty much either fab your own or get them from Europe. The engines respond to the same tweaks as the Cummins for the most part but I haven't seen many people changing injectors but rather investing mostly in performance pumps and improved induction/exhaust systems.