Who in the world would ever want such a thing? 
I think I'm the only idiot on this site who's attempted this. Getting twin-plug heads may be "easy" but getting twin-plug heads done "right" is less so. There are a lot of ways to screw it up, and a lot more to it than just jamming a second set of plugs in the chamber.
Regardless, you're right-- the heads are the easy part. Willhoit has been doing a twin-plug distributor for his engines for years, but I wasn't aware he was selling them as a part.
It's possible to covert a 009 to work with a twin-plug Datsun capo and rotor (John uses an Alfa cap and rotor), but Willhoit's setup is much more elegant and probably better all around.
The hot set-up is to do crankfire and just drive 2 coils with the ignition controller. My set-up was a hybrid-- I used a single pickup in the distributor, and drove a programmable "Black Box" modified by Mario Velotta (thedubshop.com) with two coil drivers. The engine is in pieces now-- but when it goes back together, I'll use a crank pick-up, some sort of ignition controller (the Black Box) or a MSD programmable controller or Megajolt, and just use the distributor to send the spark to the right places.
It's a cool project, and I'm in deep enough to stay committed to it-- but frankly, beyond the "gee-whiz" factor, it's a lot of work (and I do mean a LOT of work) for a smallish gain.