I have a 73 with the weber carb. Used to be the dual carbs. But, I also
have the .009 distributer, It throws a little twist in the timing
equation . i bought my bus from a fellow who did not understand VWs in
general and especially engines in particular. He paid quite a few
mechanics to time and adjust this thing so it would run. Never did get
it right so it ran like sh** by the time I rescued it from him. 
 It was no problem to set it right with nothing but a wrench and a screw
driver and a few trial and error runs up the hill by my house. 
  If you're buying a weber it may or may not already be set up to run on
your Volkswagon. Ascertain as well as you can the application for the
particular carb you get. There are a few different types. I don't know
them all. 
 The only problem i have is choke, and cold running. It starts up fine
every time but the choke element isn't having anything to do with
keeping it running while the engine is still cold, I drive with two feet
and keep a little pedal to keep it running till it warms up. Warms up in
about 25 minutes of driving that is. I'm at work by the time it settles
down. It has some fancy looking chrome air cleaner on it that doesn't
allow for preheated air coming in from anywhere. 
Ya know how every car in the world has a little hose bringing warmer air
to the carb from the exhaust area? Not here. i wonder if that would help.
 good luck 
Paul in Pittsburgh