Mike, if you're willing to make a formal complaint and back it up with a statement then the police should be duty-bound to follow it up.
They will be able to check for any locally-registered silver C63's and check the VRM's against what you believe you saw. Not difficult for them to check, trust me!! They might not find the vehicle in question but it's worth a go.
From the circumstances outlined they are not duty bound to follow it up.
No independent witnesses and at the end of the day I don't wish to sound flippant but he's only 'cut you up'.
Nobody is injured and from what has been described no chance of it even going court, never mind a conviction.
It's your word against his and without independent witnesses it's going no where and even with independents it's not serious enough to warrant prosecution.
Take it on the chin and forget about it.
I'm sure he will be in contact with the Police sooner rather than later regarding his driving.