Reply to "Fuel pressure ok?"

The app3923 might just be the platinum version of the copper plug you have. The thread and reach is the same according to their website. Take your plug along with you to the store and check the tip to the base of the washer is the same. 
It will be ok to run the car for a short while with the one odd plug but you would need to get a new set of what you had originally. They also need to be adjusted / replaced more often than platinum or iridium plugs. 
Your plug looks fouled but you need to pull your other plugs to compare. 
You could move #8 plug to a different cylinder and see what result you get before buying a plug. 
If your new plug fouls / cylinder does not get to temp, then do a compression test or leak down test. 

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