Its just a matter of soldering the new ones on, requires a good sized soldering iron at a squeeze a small flame solder and pliars
ive had 14 years of fiting them, should be able to find a similar set as for length im not sure check the springs are located ontop of the spring when assembled if they are too long the springs will be close to the edge and may slip off the side and jam them,
On Friday I went to local shop they sell all kind of starter brushes. I gave him TTR sample and they found similar set of 4 pieces just for 5€. The new brushes were thicker by 1 mm, the size was easily reduced.
The contacts of the brushes were easily soldered. Then I installed everything back and it started!!!
In addition I cleaned the air filter and went to the forest for riding. We did ~120km in the sand, gravel, forest road with full throttle and fuel ended up, then switched on reserve.
It was pulling like a hard bike and eating fuel too :) Total km on weekand ~180km with ~13l of fuel.
I have another bike Honda CBF 2008, I noticed the starter is pretty same, the numbers matches Mitsuba SM 13 12V. The only difference is the + contact it is rotated on CBF.