I did this mod last week, much as Quickbeam is describing, and drilled 2 holes through the black plastic backplate, and smoothed off the little raised portions of the black backplate. The only problem you run into is the raised mounting block that's cast into the main body must be drilled into as well, and care must be taken not to disrupt the spring clips/contacts that hold the bi-pin bulb in place (this will make more sense once you open up the headlight). Make sure not to drill the holes for the plastic Opalec legs too big, so that it says put once it's in there, then drill out the reflector. It's a fun mod, so enjoy the process
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As for the brightness, it's not quite as bright as my Princeton Tec Aurora, when the Aurora is on it's highest setting.
Using the Opalec doesn't make for the most cost-effective mod, but since the rest of the ingredients list is only $5.oo more, it's not so bad, I guess. A Streamlight Septor costs about the same, and is gonna give you lots more light, with the option to use 1, 3, or all 7 LEDs at once...but all that without voltage regulation/constant output (a feature I've come to LOVE since aquiring my Opalec).
Cheers!