Head race bearings

[Fazerider]

Fitting the bottom one to the headstock was slightly tricky now you come to mention it.
It's a tight fit, you're working at an awkward angle and being tapered there isn't much of a lip to thump on.
I used the old lower bearing to hammer against to get the new one in (temporarily glued them together with silicone sealant) and heated the bottom of the headstock with a hot air gun to expand it slightly first. The advantage from heating only lasts until the bearing is part-way in whereupon it reaches the same temperature, but when it's in far enough to stay put you can use a length of threaded rod or fit the steering stem and winch it in from the top.
The top one is easier because you can see what you're doing and gravity's not fighting you.
Fitting the bottom one to the steering stem is also straightforward: warm it up, drop it on and give it a whack using a hammer on the end of a length of plastic waste pipe.
Whether driving them in or out it's essential to keep the thing square… get it tilted and it'll jam.
So long as you're happy to improvise a few tools it's not too difficult a job.