Your opinions on this 1680 Red Submariner please.

[Storky]

I've been thinking about this Red sub. The dial is absolutely lovely and because I've looked at it for so long it looks too good to be correct .... perhaps, as we say in the UK 'I can't see the wood for the trees'!
To me a superb Mark IV dial. I've tried to look at every detail even the right hand side of the Superlative 'A' seems to have a slight curve, the same as photos I've seen.
I realise it has service hands but a nice fat font insert that I think is original.
Serial 33***** but the punched papers(!) are dated 1977 which seems to be about 4-5 years different?

Your opinions would be much appreciated.
Thanks in advance!