If you plan to get MSDS headers in the future, just wait until then and don't worry about gutting the precats. It is such a huge pain to take those stock manifolds off that once you get them back on you will never want to take them off again.
If you think those bolts on the manifolds are tough, wait until you get to the bolt on the alternator (remember, you don't have to remove the alternator, but you will likely have to rotate it to the side.) I hope you have lots of socket extensions and U-Joints because you will need them as well as some band aids.

MSDS headers are well worth it once they are on, but all that work for gutted precats is not worth the trouble IMHO, if you are planning on getting MSDS anyway.