I spoke with Roger today, his choice for most parts on a bike is 3003 h 14..which is halfhard...0 may be hard to source. He then still anneals with flame. He haqs built some prettyimpressive sheetmeetal parts for motorcycles,including fairings that have helped him set world records on the salt flats..
Franken,unless you get a tig, you can always gas weld, , it is a less hard weld anyway, and you will need a torch on hand anyway to anneal.