There are indeed corresponding marks on the piston. Not dents so much as silver marks. And it fits in with the engine being locked into TCD on pistons 1 and 4. Possibly when I was putting the camshaft locking tool in I did it. I'm so stupid! But you live and learn. Hopefully it won't be too expensive of a mistake. At least I now know what happened, despite my denials to the contrary. I couldn't have done this without all the help from everyone on here, so a big thank you to you all! It's not over yet, but hopefully the end is in sight.