440 Source Aluminum Big Block Heads

Thanks for your input. I dom't think it was anything I did when I changed the springs. Changed the locks and retainers at the same time. Valve spring heights were ok. Besides, if something was wrong from the start I don't think it would have lasted for 50 plus passes (1/4 mile) and at least 100 miles on the street. But you never know, I've blown a lot of stuff up over the years. Thanks