More than likely spot welded, If they dont protrude through the other side.
The alternative would be a captive rivet passed through the hole before the tube was pressed. The pressing additionaly holding the rivet in place.
Maybe a tad much VeeeCeee, but when one cannot be sourced, then these methods become fairly good options.
Id have no hesitation in removing the rivets via hole saw,dressing,fitting in the existing holes on the original green pair and welding in, with a final linish. 30 mins work Id reakon.
