The Amal carb bodies used on postwar Douglases are Aluminium alloy and not zinc based. Provided the damage does not extend to any of the drilled passages, your carb body can easily be welded. When riding our Comps in Vintage trials, we went through a period when we kept breaking carb bodies. I usually got the job of repairing them. I found the easiest way was to obtain a short length of 3/4" dia steel tube and then split it lengthwise. The two parts of the body can then be threaded onto the tube to keep then aligned. The welding can be done either with TIG or acetylene torch. If done with acetylene, make sure the finished job is thoroughly cleaned to remove all traces of flux. Boiling up in a pot of water will usually do it. Afterwards, a light spray of WD40 will give protection against further corrosion.
Regards,
Eddie.