I like them as overheads too - a lot. And on acoustic guitar as well. In fact, I liked them on a lot of things when I used to work at this studio with a small, dead room and cheap mic selection. Haven't had a pair of omnis since then. But I digress..
I believe this mic uses the Panasonic capsules with built-in fet that everyone else uses. The primary mod was the linkwitz capsule mod and maybe changing out the head amp. Anything to decrease the noise - that was their main weakness. Last time I checked there was TONS of info on modding this mic at recording.org, mic builders group, and the Tape Op Messageboard, but that was a year ago. Do some searching.