Pila GL4 upgrade to LED?

I've had this GL4 for a LONG time. I'm looking for a drop-in solution to get more light out of it: with fresh cells the light output is worthless. Bonus if there is a way to run 18650s with new LED.
I search the forum and there is too much and too old info. Maybe Im a bit lazy but not totally...I did try. I would consider sending this off to a Dr Flashenstein for upgrade surgery if it wasnt too expensive.
Can anyone give me the definitive word on an economical route to better light out of this thing?
Thanks

Iirc the GL4 uses a D36 dropin that "should" (?) be replaceable by standart D36 LED dropins, unless you have a LED switch instead of a clicky. Check Lumensfactory, they usualy mention if their Dropins can be used with the GL4.

They have one for the GL4.