Need some help with my engine rebuild

I just started rebuilding a 78 kz1000 that was given to me by my father. I planned on redoing everything on the bike since i have a a newer bike that i can ride while this one is being worked on. So i started by by taking everything apart and tearing apart the engine. One thing i was told was that the engine had a big bore kit put in it before my father purchased it. So my first problem is help identifying the piston that was used in it. i measured the pistons and they appear to be 72mm, so i've already determined that it should be a 1075 kit as opposed to the 1200 kit he was told was in it. but i was hoping someone on here can help identify the manufacture so i can get new piston rings for it, the only identification mark i've found on it was on the bottom side of the piston which was 4025, not sure if thats anything or just a production number. the second problem i have is that when i was disassembling the engine i found what appeared to be melted plastic around where the cam chain rides. the issue is that i can't find anything that appears to be missing or bad that would cause this. its not really a big deal since i plan on replacing a lot of the cam gears and guides that seam to be worn and hard, which is pretty much everything. i've attached a couple of pictures of the pistons, unfortunately i didn't take any pictures of the melted plastic before i cleaned it out

Is there a w anyplace inside of pistons?

Maybe the melted plastic/rubber you seen was the little dampner blocks that sit on each side of the cam chain idler gears.

Looks like an old Wiseco piston. The number on the wrist pin boss might buy you something....

You might be looking to see if No.#12 is still screwed in place, and in the correct shape at the front of the Cylinder Block.

Thanks for all the advise, I checked the pistons a little more and found that there is another mark on the other boss, but there is an hole drilled right through it on all of them, one of the them appears to be half of a w in a circle, as far as the plastic, all the idler dampener blocks seem to be whole and accounted for, and the guide was there and the correct shape, but did have some grooves worn in it, since it appears to be limited to the cam area, I'm gonna try and replace as many pieces add I can find

The w in the circle stands for wiseco