I ran into the same issue, a 650 tank and petcock with 750 carbs. To overcome the kink in the line issue I made a special t, and it seems to do the trick. Got the parts and Lowes. To get it all to fit together snuggly you'll have to chop the threads shorter and then file them down so they fit inside the T then pipe solder it all together.
Sorry, doesn't answer your question, but if you can't do the petcock thing, this is a decent alternative.
HTH
Brandon