Chimbu and mad...
I'm not really sure what the difference is between the FAR 135 and 121 ATP...I honestly thought the written is all the same. There is a flight engineers test and a dispatcher's test which I think takes from the same bank of questions as the ATP...but I'm not really sure what they entail above and beyond the normal ATP written. To convert you have to take the written. You can order a book from ASA publishing which has every question in the ATP bank...easy cf to the aussie one. To get work over here....your best bet - I hate to say it- would be instructing. There are a lot of places that need instructors. If you got a J1 visa to do that it may lead to other things, but I'm just guessing. I don't know of any companies that are sponsoring, but I haven't really checked it out either. Try somebody who flies VH- registered aircraft over here, that might get you somewhere. Sorry I can't be of more help.