From the Willhoit site:
The WR Twin Plug Distributor is a new product for converting any 356 or 912 engine to two spark plugs per cylinder. The distributor uses a Pertronix Ignitor II unit which delivers a standard 12 volt signal that is not sensitive to interference like many magnetic triggers. There is no advance in the WR Twin Plug Distributor, and it's made to be used with either a programmable MSD 6AL-2 CDI box or an EFI control unit.
Switching to a Twin Plug setup has been proven to significantly boost low and mid range throttle response, as well as allowing a one-half point higher compression ratio. It also adds a distinct look to any 356 or 912 engine.
In addition to just the distributor offered on this page, WR offers a complete Twin Plug Kit for $2,850. The kit includes this distributor, a preprogrammed and wired MSD CDI box, Magnacor plug wires, two coil options, upper and lower NGK Iridium plugs, and complete easy to follow instructions for installation. The MSD box is mounted under the passenger's side floor board and a period correct wiring harness connects it to the distributor. The entire installation is designed to look vintage and original. Please email for photos.
WR can drill your 356 heads for twin plugs using an easily available CR7HIX NGK plug. The charge is $600 per set plus shipping.
This is essentially what I did, albeit with different parts and for a lot less money.
It's adequate, but not ideal-- it is fully programmable, but the entire thing is dependent on a Pertonix (or Compu-Fire, in my case) pickup. The problem is accuracy-- there isn't very much space inside the distributor, and some sort of crank pick-up would be a lot better.
Moroso makes a "flying magnet" trigger wheel for V8 guys looking for more spark accuracy, and AJ Sims makes something similar by adapting a Pertronix pickup on a bracket, and then drilling two magnets into the crank pulley. If I do not go with a full EFI/Crank-Fire package, I'll most likely do something similar, but with an industrial proximity switch and magnets.
I agree, Robert-- there's nothing like the "bundle of snakes" look of a twin-plug distributor.