I'd start with the driver's side valve cover. It's only four bolts.
Since you mentioned changing back to the heavy valve springs from the lighter 'checker' springs, there's a pretty good possibility that the keepers on one of the springs for cylinder #1 did NOT seat correctly.
That would explain the cascade that would cause the engine to stop turning. (I hate using the word 'seized').
And to add my voice to the chorus, if you get frustrated WALK AWAY for a day or two
|