1. A good nail-brushing with washing-up liquid.
2. Soak overnight in white vinegar. Rub off loosened rust and assess if second soaking is needed.
3. Rinse under running tap.
4. Sponging with bicarbonate of soda and water to get rid of residual acidity. Rinse again.
5. Final clean-up with Barkeeper's Friend.
Next step will be repainting the words on the backs "Power Pakt" in bronze and "American Model" in red.
Awaiting @Crow to tell us a bit more about Forgan St Andrews Power Pakt irons. Maybe move this info to Vintage Golf thread.