Couple of quotes:
"Sigma however specialises in getting the best from the street stuff, so a 996R or the later more mass produced 998s, (the 2002 998S engine has the same deep sump sand cast crankcases (made in super tough Galsi 7 alloy) as the homologation engines but with the mass production side of the motor just a little more finished) was going to be in our future."
http://www.sigmaperformance.com/testastretta.html "The new Testastretta engine finds its way into the std models for the 2002 model year. The 998S that everyone except those in the USA gets has the same engine as the ‘01 996R. The ’02 998R has a bigger bore/shorter stroke 999 engine."
http://www.moto-one.com.au/performance/998s.html