"what's the hand throttle? Literally like a plane? Which cars had that - and why? Cold start idle? Neat!"
It was for a higher idle during cold starts. Some people may occasionally use it like a manual cruise control during highway driving on flat road if they get a leg cramp.
I've never liked cruise control because I feel seperated from the driving experience and not in as much control of the car.
edit: Hand throttles were in the early seventies 911's, I don't know when they started and stopped putting them in. There were a couple different types. One was on the left side of the emergency brake lever and another was farther forward on the tunnel where a center console would be on later cars. You would have to lean forward to reach it so the one on the left side of the emergency brake lever seems nicer.
The later 9 position knob servo motor auto heat boxes may be discontinued, I couldn't find one on pelican parts but I know they used to have them.. so you could probably make some money by backdating to the emergency brake handle with heater levers and selling it to someone wanting one if it's in nice condition and working right.
It does look like you need to replace the cables to the diverter valves when backdating to the levers. They're about $12 each.
Here's another 9 position one on ebay.
http://www.ebay.com/itm/Porsche-911-Heat-Control-Unit-/161196628612?_trksid=p2054897.l4275