Your own piston (pic. #1) has 025 on it. That means this is 0.025mm (or 10 thou) oversize. That means your engine has been rebored to the next size from std to 025 oversize. Good thing is that you still have enough life in your engine to go 20 thou, 30 thou and maybe 40 thou. (I am not sure about the last oversize limit - 40 thou). You have only shown one of your own pistons. What is the condition of the other one? In order to establish if your existing pistons can be reused, you need to check the ring grooves for excessive gap, gudgeon pin for excessive play, piston skirts for scouring and the piston face for valve slap. Insert the piston in the bore and check the clearance between the piston skirt and the cylinder bore. Please note that piston skirts are oval, clearance is taken at the tighter side i.e. front and back of the engine facing forward.
If you are thinking of going with the Kawasaki pistons, compare the weight of your original piston vs. Kawasaki piston (a jeweller's shop scale will do). Also check piston crown height (gudgeon pin centre to top of piston crown) BTW, CB350 piston have deeper valve recess in the piston crown, this could mean if you fit Kawasaki pistons, you may end up with lower compression ratio or piston hitting the valves. I can't say which from the pictures. In any case a lot of measurements and calculations have to be done of you decide to use the Kawasaki pistons. Pic, # 5 - Good to see you have a new camshaft. For seals, Longman Rubber Store in Pindi is the place to go. You will be surprised to see the other strange stuff they have there.
Overall so far so good.
