secondary voltage question

Yes,
I'm betting its ignition wire(s) or plug(s).
If I remember correctly, the tall spike voltage on the scope would indicat resistance, like what you may have seen on #7.
Before you start chasing your tail,
the used plugs tell the story, it should indicate which cylinder may be missing.
Before you go all out swapping things, I would systematically rule out the secondary ignition system:
- Check inside distributor for signs of carbon tracking.
- Remove and compare all plugs, especially #7 to the others.
- Replace that single #7 plug and that plug wire first, with new ones.
- Run engine to test it again.
If that doesn't get positive results.
-replace all 8 plugs and all wires, including coil wire.
Then, if it still misses, you can move onto compression checks, fuel, etc.