Must be very strong sandpaper LOL
The Heart stamped frames were Tanges. I had this discusion with Spacefruit, but couldn't remember whether the hole in the ET was a flat circle in the gusset, or whether it actually had a slightly raised "bezzle" around it. In any case, some careful drilling and filing would be possible. But I guess it would be better to clamp it all in a pillar drill with some sacrificial material tacked in to stop the drill mullering the gusset.