I'm pretty sure that Streamlight doesn't sell the LED head separately. You would need to buy a whole new LED light.
That said, I think the Strion LED is an excellent light. There's really not much to it. The UI is simple, the modes are useful, and it has a forward clicky tail switch. The real advantage is that you can use your existing Strion charger with the LED version, so you can save a few bucks by buying one without a charger.
A buddy of mine who's a cop asked me for a flashlight recommendation recently. He'd lost his 6P that I upgraded for him with a 17670 and a cheap DX dropin. I recommended the Strion LED, and he loves that light. He's constantly raving about how great it is.
My only beef with the Strion LED is the strobe function, which is a matter of taste.
Good luck!
-John
