My only idea would be to get a stock backbox from the scrappies, cut off the mounts and weld them onto the universal box in the same place , that is my current idea unless a wild sportex appears for cheap
I cut my std backbox off, then cut both ends off and emptied it so it was like a tube with hangers. I then cut it into halves, along the length, cutting top and bottom. Then all I had to do was wrap it around universal backbox and secure with plenty of cable ties. Ta dah! Std hangers on universal bacbox
It is absolutely solid and fits great. I will be changing cable ties for metal cable ties or weld bands around sleeve when funds allow. Cable tie engineering ftw!