Regarding using one of Jan’s LED retro-fit bulbs…They might work. I haven’t seen one up close, but they would have to be the same size as a normal bulb, so there would be room, if you could finangle a way to mount the bulb that was electrically isolated from the rest of the housing, which honestly sounds like more trouble than it’s worth. If you’re going through the trouble to spend this much on a taillight from japan only to tear its guts out and put more money into, maybe you should look at other options.
I’m in the process of trying to solve this lens problem, I’ll report back when I have some answers.

Also, is the frame mounting stud M5 or M6?

Thanks for presenting your analysis of this light, I may have to consider it for my next project.

@Dan: I met you a while back while you were down in Olympia, thanks for the kind words. The electronics in this light are tamper-proof and there really isn’t enough room to add anything but what was designed to fit. Definitely no room for a standlight. I’ve had a couple conversations with Mitch Pryor of MAP cycles down in Portland about making a small run of seat-tube mount taillights like this only better. We’re still thinking about what to do about the lenses.

In your review you mentioned that the plastic housing is “slick” and tamper-proof. Do you think it’s possible to build a different LED and standlight into this housing?

BTW, I am a friend of Corey Thompson and found your blog through his Picasa picture galleries. I’ve been very impressed with your work retro-fitting the vintage light housings.

I’ve done a few, but nothing as clean and tidy as yours. I was cannibalizing the guts from Busch & Mueller Seculite Plus fender-mount tail lights, which are pretty bulky. This really limits the minimum size of the housing.

I’d be curious to hear your opinions on re-fitting these Kimura lights. Thanks for your time and for sharing your process.