Interesting. Okay, a few more comments...
Why did you build an engine like this, and not install new valve springs? You are very lucky that you only damaged one valve, and that the piston didn't get hurt.
It's not possible to determine an engines compression ratio with a gauge. There is only one way, and it's through math. When you perform a compression check, you are only checking the cranking compression, not the compression ratio. They are two different things.
A cam with .501 lift is small/average, even for an otherwise stock engine, but for one with 12:1 pistons, it's tiny. You could have gone significantly larger without much of a vacuum problem, and even bigger if you added a vacuum canister. Just food for thought for your next project.
On a side note, Dino is right about a spark problem usually effecting the entire rpm range, except when it's a coil that's failing. Coils can be a real PITA sometimes, especially for something that is really so simple.
If I were you, I would pull both heads, and have all the valves checked. Then I would install some new springs so the valves didn't float again.
But that's just me.
Take care,
~Chris
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