After a long wait for an ESC I have finally installed the RC gear in the Mercedes SLS. I have used a Spektrum MR200 receiver I had ekstra, Then I bought a 10A brushed ESC off Amazon and used that. The ESCs I had ordered on ebay weren't showing up so I ended buying the ESC on Amazon. (After I installed the ESC, all the ebay ESCs arrived a few days later). Finally I had a micro servo lying around that I used for the steering. The original motor was re-used. I didn't try to remove it. It seems tricky to remove the motor.
Normally the car will be running on 5 AA cells, but it should be capable of a 2 cell LiPo. At least I used a 2S LiPo in testing. The only thing is whether the motor can handle a 2S LiPo? I don't have the answer for that.
I had to do some modifications to the steering to be able to use a servo for control. I ended up connecting the steering arms with a turnbuckle and connect the servo to one of the steering arms. This took some modification to the steering arms, so I won't be able to return to the original configuration.
Thanks for looking :)