Maybe this just isn't the job for you? If I were in your shoes, I'd be thinking less about the existing code, and more about what it does, and any edge cases, I would also review the code of your peers to see if they're just verbatim copying it, or if they're just making sure that you get the same output you need.

Another thing you could do is, become the guy who builds all the documentation for the new codebase + unit tests. If you're confirming the two code bases are "exact" you will need a lot of testing.