Looks like its been timed up wrong tbh

What cams were in it ?

Check the valves to make sure they are not bent, probably not but worth checking before you put it together.

Also water ( I believe ) would cause everything to look so clean so might of had a head gasket failure as it would be a bit strange for someone to clean only 2 pistons if they had pulled it apart for any reason before you got it.

No idea on head thickness, 138mm springs to mind as a ok figure but I am sure someone can confirm the minimum height, either way if its low you can use a thicker gasket to get over that