Fujinon EP are 6 element, 4 group lenses
source here. ES are 4 element, 3 group. (and yes, ES<EP<EX)
"EL-Nikkor" could mean anything, they didn't change the name when they upgraded the formulae, you'd have to post a photo so we can identify which it is. (although if you've got the original box, they were stamped with 'N', but afaik the lenses weren't. My lens isn't marked 'N' but my box is, but no guarantee it's the right box for the right lens).
I
think that the f/2.8 Nikkors were the new 6/4 versions and f/4 are older 4/3, but there are probably exceptions even if this is roughly true.
Edit: Wikipedia has f/2.8 N as 6/4 Double Gauss, and f/4 N as 4/3 tessars, the non-N f/5.6 in longer lengths are 6/4 Orthometar and nothing said about shoter non-Ns. And as is the problem with them thar wikis, there's no source listed.