You messed up your link. It doesn't work with the "a" attached. This is correct...... http://www.meridiantactical.com/sf5wledmocok.html
I am sure that you meant to say "Will the kl5 head fit on c3?" As for the answer, I don't know. It has been designed for the M2, which is probably old news for you.
I hope that when the other sleepy members wake up on Sunday morning, they will give you an answer.
The KL5 should not be powered by three SF123As.
That's the official line.
I've run one of the KL5's I have on three SF123As since I got it. It's only had about three or four battery changes. To be honest I don't see significant difference at all to be worth 'risking' it.
IMHO, the best thing for a C3 is a KT2. Or at the very least an M2 bezel. It looks much better.