Just stripped down the gun and got stuck in.
Got all the marks and scratches out with 320 emery paper.
Then went onto W&D paper, down to 2000.
MicroMesh down to 8000.
Then polished with Autosol.
I resisted the urge to cut or buff on a wheel and stuck to hand work only with sanding block and fingers.
I must say this stainless steel is very hard and even the shallowest scratches needed quite a bit of effort.
Took 4 hours to work over the whole frame.
The gun now looks very nice indeed with no obvious marks, just a nice shiny clean revolver
Thanks for the advice.