My FG84D OEM tank has that lug too.my tanks have a locating block on the bottom which sits in the J bracket to prevent the tank from spinning or creeping
would have thought that was standard
the OEM fuso "radiator tanks" are the only round tanks that i have seen that have that lug. most other tanks are made to be univeral fit, so would be a bit hard, because the J-bracket spacing will be slightly different on each different vehicle.