With a single 44IDF, you are probably using an aluminum or cast intake...no problem there.
See if you can find a Weber supplier for the Type 4 engine. The VW Fastback and Squareback versions had the engine mounted under the rear compartment, so the air cleaners had to be low profile.
As far as engine displacement, probably stock 1600cc (1585 according to VW), although with a 44IDF you could probably run a 1641, 1776, 1835 or 1920cc engine.
I would check the ignition coil. Mine would run flat and eventually eat the coil for lunch (actually, several) until I got the Bosch Blue coil.
You may also have a vacuum advance problem if you are using the stock distributor...if you don't know see if any hoses emanate from the distributor...actually the round thingy attached to the right side of the distributor.
If you have neither...you have a Bosch .009. It a centrifugal advance versus vacuum advance style.
You should be running copper Bosch plugs as well. The platinums don't work well with the air-cooled VW motors nor early MBs...
Take a pic of the motor...I can tell a lot from a good pic...
