Most header systems are designed to mate to their own midpipe. Collector location will vary depending on where the mfr thinks it should be for the state of tune they're aiming for and methods of connecting the the mid-pipe to the collector can vary, as well as how the pipes route, so most of the time, you can't mix-n-match parts from different systems.
If you're looking to replace your stock header with another stock header, one from any B12 will work - if you have a B12. Any B6 header will work for you if you have a B6. (The B6 has slightly shorter tubes to match the slightly shorter engine height.)