Nope, might be slightly less. The 5.4 V8 M113 in the CLK55 I have is only rated at 255kW/342hp (347PS).
I think the W210 E55 has marginally higher output 260kW/349hp (354PS). I'm not sure if the engine is physically any different power-wise. The increased power might be a difference in the exhaust system or vehicle-specific map stored in the ECU.
Bearing in mind that most conversions use the original ECU from the 4.3 engine and the same C43 exhaust system I doubt the power should be any higher than that in a E55, possibly lower.