The cylinder interior color is grayish. That's a sign of Alusil cylinders. Nikasil are slightly yellowish.
Also take a look at the lettering on the side of the cylinder. Mahle nikasil clearly say Mahle and KS alusil cylinders have a "stacked" KS logo like this.
Used KS piston & cylinder sets are pretty common and sold rather cheaply. So maybe you can get a complete replacement set. Seems like a lot of people ditch the KS stuff and get new Mahle or they'll have the alusil cylinders plated with nikasil and use JE or CP Carrillo pistons in them. EBS Racing is well known for providing this service of "converting" Alusil cylinders to nikasil. Not sure if they use US Chrome or Millenium Technologies to do this plating
Make sure your measurements are very precise (use an actual bore gauge with a 0.0001" resolution dial indicator) because the clearance between the piston and cylinder are very tight. If you're not measuring accurately, your clearance can be way off and you'll have a bad situation on your hands rather quickly when the engine is run. That is, if your clearance is too tight. If it's too loose, that's not good either. But much better than being too tight!
Edit: By the way I have the '84-'87 factory Porsche tech spec book in electronic format that you can download. Shoot me an email and i'll share it with you from my google drive.
