Greets, sb56637. It always blows my my mind just how frugal you are: no P60 hosts yet! Kind of like how it surprised me that good old4570 buys Shiningbeam forward clickies by the 5-pack, yet never bought a McClicky. I have a friendly competition with a friend on who is more frugal--I think if I brought you in, you'd win!
What you call a crown, I call a bezel ring above. And yes, they do indeed unscrew. Thankfully! Allows you to get a smooth or "attack" (defensive) bezel, replace the glass disk (I hate calling it a "lens", but... can't come up with a better word). Or... go without a 'lens' at all, nor bezel, for maximum light transmission (at the risk of getting dirt in there, especially in the pocket or on outings--best to store face-down if you do). Old4570 has actually done lightbox tests comparing Bezel vs no Bezel, and has empirically proved that the bezel does indeed block some light (in the form of spill). So no, if you don't want to 'upgrade' the bezel to a plain smooth ring, and don't like the crenelated bezel, you can go lens-less (and "bezel-less"), and you'll still have the reflector of course (which will then get a little dusty, or worse... but usually no big deal).
Where did you see the L2i body for $7.99? Be careful, usually at that price it's just a battery tube: no head or tailcap. If you have another Solarforce or compatible model (the 504B is one of the few which would work), you could always swap the tube in, when you wanted to use AAA's. But that gets frustrating. I just checked Ebay, and the cheapest price on a complete L2i host is $10.56 delivered.
18700 fitting with no modifications in an L2i, not L2... well, I can fit my over-length Soshine "18650" protected cells in my L2i, IF I:
-unscrew the head somewhat
- don't fully screw in the tailcap
So, I think yes, if you're okay with things not being fully screwed-down. You can only unscrew the head so much, before the outside spring of the drop-in isn't being held against the shoulder of the battery tube anymore, but I suppose that could be stretched a bit to get it even further... but that would qualify as a mod, wouldn't it? :) . The L2 or L2P would be a better fit. No problems with the Soshine batteries in those with everyday switches. But L2 does not tailstand with its included switch. The L2P does.
And yes my L2i does tailstand (just tried it).