Re: E55amg
Hi Jonny
Changing the fuel pump will be the easiest part.
The Crossfire TCU will need to be reprogrammed for the different transmission ratios in the SL transmission. (The V6 and V8/SRT transmissions have different ratios). If you go to drive it without reprogramming the TCU, it will go into limp home mode as soon as it changes into 3rd gear. I had mine reprogrammed by Eurocharged, you'll also need to tell them what diff ratio you are running.
Put a wavetrac centre in the diff.
You'll need to change the driveshaft (at least the front section) as the connection to the gearbox is different. You can use the front section of an SRT6/SLK32, or change the connection on the transmission.
You can modify the existing exhaust headers (weld the front part of the V8 headers to the rear of your existing V6 headers) or buy new ones that will bolt straight on from Needswings.
Lower the front swaybar to clear the front of the engine sump. Just use some large washers as spacers.
As your in the UK, your car will be right hand drive. One of the biggest problems I had was the the M113 engine has the starter motor located on the right hand side. It's where the steering box is and will not fit. I had to relocate the starter to the left hand side of the engine (lots of work!). You can reuse the starter from your V6 as its the correct type for left hand side mounting. Have a quick look at your V8 and check where the starter is.
The main issue will be the ECU. The ECU needs to have all the right circuitry to run the M113K engine and work with the Crossfire chassis. It needs the right firmware and must be coded to suit your vehicle options. It also needs to be mated to the immobilizer in your car.
Put bigger brakes on it.
I'm not sure about the vehicle modification laws in the UK, but if they're similar to Australia, the maximum allowable engine capacity is based on the vehicle weight. NA engines have a multiplier of 5x and forced induction engines have a multiplier of 3x. I wasn't able to legally fit the supercharged V8, I had to use the NA version. It would pay to check before you go to all this trouble (unless you just want to have a track or drag car).
Good Luck!