peanut head plugs

I was looking at my stash of slant plugs, and I noticed the difference in length of the NGK ZFR5N vs the NGK UR-4...... looks like one is 3/8 or maybe 1/2 inch further into the head than the other. The UR-4 being the shorter one\
I have a peanut head on 2 cars, O Reilly shows the ur-4 as a choice, and seems like slantsixdan was always praising the ZFR5N, but maybe it was for the drool tube type head???????
Are these longer and shorter plugs interchangeable on the slant heads or what????????