How to tell if engine was replaced

[JMP]

Dear Forum, I bought a 99 Boxster w/ Triptronic. It has over 117,000 miles on it and it runs and drives like a new car. No oil leaks or any engine problems whatsoever. I have heard that early model Boxsters had engine problems and some engines were replaced under warranty. My question is - is there a way to tell if the engine has been replaced? Like maybe by finding the engine numbers or something. I got the original owners manual and service book. It appears that it was regularly serviced by Porsche but no mention of an engine replacement. If you can tell by the engine number - can anyone advise were to find it on the engine.? Thank you very much, Jerry Peterson