With respect, why attempt to repair Mg wheels? Most of us have replicas, not original Cobras, and aluminium alloy wheels can be made to look like authentic vintage Mg wheels, so why not err on the side of safety and stick with aluminium alloy wheels?
nota bene...a 275/60 x 15 tyre weighs around 30lb / 14kg, and a 15" x 9.5" aluminium alloy wheel is
only around 15lb / 7kg
That said, I understand the desire to go as "authentic" as possible in certain areas.....but if safety is a concern....
Cheers, and stay safe!
Glen