What do want to know?
In your first post and again 07-18-2021 10:10am: you asked about a nominal speaker spec (8 Ohm) vs a DC spec.
Again: if your 18" woofers came out of either EV Six or 400 systems: an amplifier's outputs will see a nominal impedance of 8 Ohms, playing music into them.
Why are you concerned about EV's magnet structures and materials, specifically?
Are you going to horn load your 18" driver?
That's the only case in which you should concern yourself, as regards any K Series, EV driver. They were designed only for horn-loaded output and a very limited, rear enclosure volume, which controls/restricts their cone motion/excursion.
ie: Note how narrow the aperture is, in the woofer mounting baffle of the following corner horn.
http://wp.volvotreter.de/projects/khorn/