Gary Mac

Hello, new here, have been lurking for a little while and learning about a car we recently acquired, Its a 48 Plymouth Suburban, its the first Mopar we have owned (I have a few Flathead Ford V8 cars and have built and hopped up quite a few of them over the years though so am not new to this) After going through the brakes, electrics and a bunch of other stuff on the Plymouth we started using the car before this (picture) happened when shifting from 2nd to 3rd. Have never seen anything like it in all my years of building and driving cars, I was actually expecting to find a hole in the piston crown from the way the engine was running but couldn't believe what I was looking at! This is as far as I have got with tear down, it looks like the engine has been rebuilt before as it's 30 over so my initial thoughts is just that it was a badly made or poor quality piston, as it was running fine up until this. It's not a fresh rebuild though so why it decided to fail when it did is up to now, a mystery. I intend to keep the Flathead and rebuild it and go through the transmission too, problem is being in England I have to import the parts, so the question is who has the best quality parts for these? I've looked at Kanter, Egge and Rock Auto who list Sealed Power pistons. Are there any other options? and are there any suppliers selling transmission parts? Thanks