engine life of raced production engines

[Roninho]

Hi,
a few days ago i started a topic in the sportcars/gt segment of this forum on what changes OEMS/manufactureres make to the racing engines that are production based engines. Such as the engines that are used in GT3 (which if i am not mistaken all need to be based on a production model engine).

Basically the conclusion from that discussion (for me at least) was that the OEMs do change a lot to these production engines.
The only racing car that i know that used a non-modified production engine is the Reiter prepared Lamborghini Murcielago (http://www.lambocars.com/murcielago/...p670_r-sv.html)

So my question is, if these manufacturers change that much to these engines are unmodified production engines not capable of being raced without modifications?
If i take a Mercedes SLS AMG or Nissan GTR (both over 500 hp), have it raced by a professional driver and have that guy race it for 45 laps (a F1GP distance ) at Spa-Francorchamps will the engine then fail?
Or if the same driver goes to the oval @ lausitzring or Rockingham UK and runs it for 500 miles on the oval? Will the engine then fail?