These were an AMG special, they weren't built with the 55 engine, you had to buy a 43 and then take the car back to AMG Germany to have the 55 running gear fitted a full conversion was around 31,000 euros with the optional 18" alloys. They fitted a 354bhp m113 v8, with an e55 gearbox, diff, and drive shafts, the floor pan of the 202 has to be altered to fit the diff as it is bigger than a 43 item, the speed limiter was also removed. This version became available to compete with a new more powerful M3 being available.
It would still appear on the logbook as a C43 but with an engine capacity of 5.4, this is also how my car appears on the logbook, and on the EPC all C43's appear as C43/55.
This is a genuine AMG 55 car I believe Will knows the car/owner.
There were IIRC less than 50 saloons and estates of these ever produced world wide, there is an article on Wikipedia that is quite good.