The stator is just a tight fit into the housing .
I would remove the stator from the engine before proceeding .
Once removed from the engine, a little tapping with a rubber/plastic hammer should get it loosened up to where it separates .
Also, once you get the stator removed from the housing, the bolts that hold the brush holder to the housing, have special fiber washer/spacer's to keep the bolts from touching the housing, note how these are placed, or your alternator won't charge if the bolts aren't put back together correctly .