Okay, guys, here's a relatively simple way to implement a left hand throttle
in a 320/360.  I have this half done, then decided to shelve the idea, but
then saw a variant of the idea implemented in Bart Bartholomew's 320 (N320BB)
for which Chuck Brenner provided some builder support.

First thing to ask is whether the left had throttle will be the only control
(as it is in Bart's airplane) or will it be a secondary control, with the
primary still in the center (as it will be on mine if I decide to finish the
installation).  

If it is the only control, you need to have a friction lock there and
probably want all three controls (prop, mixture and throttle) together by
your left knee.  If it is a secondary control then you DON'T want the
friction lock (the one on the primary knob is enough) and you probably only
need the throttle control duplicated on the left side.  Including all of them
makes for a bulky installation (but Bart says it doesn't get in the way).

Go to Van's Aircraft and buy a throttle quadrant.  Either use it as supplied
(three levers plus friction lock) or strip it down to a thinner one-lever
quadrant and remove the friction lock (as I have).  Glass a wooden or
phenolic block to the left hand inner wall of the cockpit to bolt the
quadrant onto.

If it's your only control, just run the cables normally.  (Bart actually has
pushrods.)

If it's your secondary control, run a sleeved control cable (just like a
throttle cable but without the knob on the end) from the quadrant forward to
the firewall, then along the firewall and back along the pilot's side of the
nose gear tunnel so that it's in a big U shape.  Mount a metal idler arm with
a central pivot point to the side of the nose gear tunnel.  Attach the idler
arm to the nose gear tunnel in a similar manner to the aileron pushrod idler
that's attached to the main spar in the wheel well (or use a Click-Bond
stud).  Make sure there's a bearing in the attachment, just like the aileron
pushrod idler.  Attach the end of the cable to one end of the idler arm.  
Now, take your primary throttle control cable, throw it away, and buy another
identical one that's really short.  Attach the forward end of this cable to
the other end of the idler arm.

Why the idler arm?  When you push the primary throttle cable in, the other
end moves towards the front of the plane.  When you push the secondary
left-hand throttle lever forward, the other end of its cable moves towards
the back of the plane (because of the U shaped bend).  The idler arm,
however, moves the same way regardless of which control is used.

Now that you've got an idler arm that wiggles back and forth, you need a
third cable which goes from one end of the idler to the engine.  This is the
cable that penetrates the firewall.  Attach this to the end that the primary
control goes to, since that's the end that goes forward when you want to go
faster.  If you're clever, you'll attach it to the same hole that the primary
cable connects to, such that if the idler arm totally fails (as in rips off
of the nose gear tunnel wall), you still have a viable connection to the
engine from the primary control.

Wish I had pictures, but I haven't built it yet.  I may not, since all my
pilot buddies say that I'll adapt to a left hand stick in less than an hour.  
After all, I fly yoke-equipped airplanes with my left hand already....

- Rob Wolf