I bought an extended threaded barrel so I could use an SWR HEMS-2 suppressor with my Springfield MC Operator 1911 pistol, but the threaded barrel I got is oversized and needs to be fitted to my pistol.  How easy is it to properly fit this oversized barrel myself?

Where is a match barrel oversized?  The barrel hood, the lugs, and the front for the bushing, right?  Any other places I'm overlooking?

The answer to how easy it is to properly fit it is this:  it's one of the most difficult things to do on a 1911.   You might get it fit so that it works, but to fit it properly, you need a bottom lug cutter, a parallell round file for the bottom lugs, a safe sided top lug file, a bushing reamer, possibly a lathe, and possibly a chamber reamer.  

Most are oversized in the areas you mentioned.  The hood should be oversized in width and length.  Also, it might be short chambered.  The top lugs are usually oversized, and require deepening, as well as shortening the height many times to get a barrel centered with the firing pin.  The bottom lugs, or feet, are oversized, and require a special cutter to fit it to the slide stop, plus the parallel file to get the last 5% or so.  Finally, most are either oversized at the muzzle with a step down, or are oversized all the way back to the chamber.  If it's the latter, you will need to put it on a lathe and cut a step down.  You will most likely need a bushing reamer if you have a match bushing, and will also need to reduce the bushing O.D. on a lathe.  

There are some addtional tools some smiths use.  I use modeling clay to guage my top lug depth by making an imprint of the slide lug cuts.  There are also some other things that I do to the slide, like prep it with a lug iron, and I lightly hone the inside of the slide.  

To me, fitting a match barrel is the most important and time consuming job on a 1911, much more so than say hand cut checkering, or other complicated tasks.  I'm not saying you can't get it right the first time, but the chances are slim.  I did only because I had a smith with decades of experience letting me use his tools, and basically holding my hand.  Unless you have a resource like that, send it to a smith.  Either way, good luck.

Thanks for the advice.  I will take/send it to a competent 1911 gunsmith.