The former owner of my P30 put in a 2002 ish Vortec 5.7L Engine. (presumable out of a Chevy Express Van)
It's running somewhat fine, but I'm chasing a misfire for few months. I pulled the plugs before and they looked fine.
Now I ordered plugs to the engine code, and guess what came:

The new Plugs have more threads then the ones which are in the engine. So which are the correct ones?

It's hard to see, but I think those Iron Vortec heads have more threads then the old Small Block heads.
Any suggestions how to measure the correct depth of the spark plug thread? I'm a Electronic/Code Monkey and could need a idea how to measure the reach in the cylinder head.

What other issues could come from running the wrong plugs?
I'm going to get a spark plug chaser and tap the holes in the cylinder head to get the deposits out of the threads.
Since this is a drop in engine conversion with no documentation, I don't know what plug should go in there.