Mercedes engines dont need to Rev, they develop good torque. if you want a tach that reads 9000 get a Honda, they cant do anything thus need all kinds of RPMs to move. But, if you like tearing into engines and junk, get it balanced, titanium rods and rings, nice high compression pistons, billet crank, bore it if you want. Paying someone else is no fun and not rewarding, i think, they built the car so you dont really get any bragging rights. Just get someone else to do the machine work and make the parts. I read about a Jaguar got 50HP just from engine balance, but I bet Mercedes are in better shape. Searching on the internet are people who make what you need. Labor is where most of the money goes anyway. It can be fairly cheap if you do it yourself. And like ADAM said it will be custom but not really all that hard, an engines an engine. 20K sounds like a lot, but it can go about as far as you want to stretch it. I'd bet more would be spent on a decent trans. to handle it all.

Heres a thought, if the C36 gets about 270HP and the V12 is two 104's of 3.0,bore it to about 7.2 litres (or two 3.6's), then thats 540HP. The C36 is pretty reliable isnt it? Machine work is usually about half of what Renntech wants, just find a good shop. I'm in So. Cal. so i can find a gazillion places, I dunno about the rest of the country though.