If you broke a ring land you would have alot of smoke. TR6's are very weak plugs which make them good because they will break from detonation before the engine will. If you had put in motorcraft plugs with the same heat range then you would have destroyed your engine.

 

how did the debris get from one cylinder to another? maybe im missing something. i agree with oxford i think that you just detonated from having to lean a fuel mixture, and thats what damaged the plugs. best to let the shop check it out though, good luck.