Whan,
The E320 coupe should perform nearly identically to the sedan of the same year. (0-60 in the 8.0 ballpark, 1/4 high 15's-low 16's) It is electronically limited to 130mph if memory serves.

The M104 can be converted to 3.6 liters for 5 figures from most tuners but that is a bit pricey. There were some twin-turbo kits out there that put HP up around 305HP with a similar increase in torque. Those kits were around $7,500 + labor. Try giving Mosselman or Kleeman a call. (if you get in touch with them let me know what they say)

Hope this helps...Lee