Getting the races out of the headstock should be straight forward as long as you have a little bit of lip visible to thump with whatever long, blunt steel thing you have to hand.
Getting the bearing off of the stem is a bit different. Personally I strip it down till I've got the stem with the old bearing still attched / fitted and get the local dealer to cut it off.
Fitting the races, I use a home made tool to squeeze them in straight to start with then finish them off with a soft drift till they are fully seated in the stem - the sound changes when they are fully home. The home made tool is a length of 10mm threaded bar and some sturdy bits of steel plate that actually contact the races. A couple of nuts screwed down & up the threaded bar do the trick of squeezing the races home, keeping all level as they do of course.
The stem I put in the freezer for an hour or two and just before that time is up I heat up the bearing in the oven. The tolerances are such that the bearing should virtually slip dowm the stem. Finish it off with a suitably sized socket that only contacts the inner part of the bearing and tap it down the final few mm.
Steve T