I've been lucky with most of my tanks, just took them to my local radiator place, St Marys Radiator Repair, Great Western hwy St Marys
He puts em in a bath for a while, not sure if it's a pickle or not, then if they leak when he puts air through it, he solders them up.
Depending on the age of the Hearse, there is this joint, I think they go back to '67
http://www.autopartswarehouse.com/shop_parts/fuel_tank/chrysler.htmlmaybe able to land one in Aus in a timely fashion
"Better tell him to get one with a silk lining next time"
Gary