Unfortunately, I don't have any photos of this repair but I can describe the process from my notes. I think the trouble all started with a hasty repair I made at an event years earlier and forgot.
When removing the 280's forks for use on my wife's EM 5.7, I discovered the top triple clamp nut and steering stem were galled together. It took great effort to separate them, and both threads were in bad shape. There was no way it was going back together without significant repair. Although the nut may be available as a GasGas part, I decided to buy an M20 x 1.0 tap and die instead. The die was needed to repair the steering stem thread and I made a new nut using the tap.
I also discovered that the bottom tapered roller bearing was in bad shape due to dirt intrusion. It has a 42mm OD and a 20mm ID (which is a standard 32004 tapered roller bearing that is readily available).
It was very difficult to remove both the old bearing from the triple clamp and the outer race from the headstock. I tried a bearing separator on the inner race (after repeated heating with a propane torch and the penetrant PB B'laster). But the separator could not get “under” the bearing, so it just mangled the cage.
Seeing no way to pull the inner race off without damaging the triple clamp, I used my smallest air grinder and a cutoff wheel (1" diameter, 0.040" wide). It was tedious to cut off the bearing's inner race. There was no room to make a single straight cut. I had to carve perpendicular to the steering stem a little at a time.
It was comparatively easy to install the new bearing. I put the aluminum triple clamp in a freezer. The bottom of the steering stem (where bearing seats) has an OD 0.7879" (the top was smaller at 0.7861"). The bearing's ID was 0.7868". So there was clearance at the top and interference at the bottom. I heated the bearing on an electric skillet to about 275° F.
I had intended to just leave the old outer race in the headstock, but it was quite worn and the new bearing felt notchy in it. Because it's aluminum, the headstock has a much smaller ID than the bearing's OD. This made it impossible to use a drift from the top side.
I then resorted to my blind bearing puller (expanded as large as it would go, ~33mm) after warming the headstock with an electric heat gun until it was too hot to touch. The bearing race came out with several good slams.
The bearing's OD measured 1.6534". The headstock's seating diameter measured 1.6523". That's about 1 thousandth of an inch interference. When heated, the aluminum headstock expanded to provide about 1 thou of clearance.
Installing the new bearing outer race was the most difficult part of the job. I made a brass plug in the lathe that could draw the outer race up using a 1/2 - 13 threaded rod through the headstock. Again, I heated the aluminum headstock with the heat gun. This worked well but I could only get the bearing race to go flush with the bottom of the headstock because the brass plug hit the ID of the headstock.
I ended up using the triple clamp stem and nut to gently pull the bearing race the final 1/8" (after again using the heat gun).