Spark Plug Confusion

I am sorry to create another thread about the spark plug thing but the more I read about it the more I get confused.
I own a '74 built 225 Slant Six (2806830-7 block if that helps) built in Newark.
I recently got told I have to remove the spark plug washers, thats not the problem, but my problem is the spark plug itself.
I had ordered two sets on rockauto.com like 2 years ago which seemed to be the ones I needed. Those were some NGK6630 UR4 // NGK7401 UR4IX Iridium. These were listed for the /6 on rockauto.com
In this forum I got recommended ZFR5N or B7ES without the washers, but none of them are listed for the '74 Valiant on summitracing.com, not even the ones I ordered earlier.
Currently installed are W16EXR-U but with the washers but it leaks oil there.