Clarification on: C2->M2-->L5

Thank you to all here helping me expand my knowledge on superlights.
I am trying to build my dream light.

C2 plus M2 head and extra tailcap O-ring make it an M2.
By replacing the M2 head with a KL5 plus a Z58 clickie makes it a L5. Am I correct?

My question: If all these lights look the same colour, olive drab AH?
They all use the same lanyard and nylon holster? if so which?
Should this new LED conversion yield identical run times, size, brightness, throw and bean pattern?
What about its ability to use rechargables? I am lost there.

Can I reverse the process, meaning putting an M2 head on a L5 making it incandescent?

Yes to all your questions about swapping parts. Some of the SF brand holsters do allow for bezel down carry with the standard head, and that would work with the C2 only, as the M2 and KL5 bezels are larger. I'm not familiar with the different models.
Z33 lanyard kit, or Z26 lanyard ring plus your choice of lanyards-same for all three. They all have the same body.
The KL5 should have a larger spot, and brighter spill, in exchange for less beam intensity and throw compared to the incans. It will maintain its brightness where the incans will steadily dim, so makes better use of primary cells. You can use R123s, 17670, or 18650(if you get the body reamed out, as some have done around here) with the KL5.
2 unprotected R123s with 9V lamp assemblies from SureFire, Wolf-Eyes, or Digilight is another rechargeable option(my personal preference), along with 3.7V LAs from Wolf-Eyes, or AW in the dealer forum running off the 17670 or 18650. I have not tried the AW or the newer WE 3.7V lamps, so can't comment on them.