Exhaust - Non Endorsable - £30 fine, no points
No Indicators - Non Endorsable - £30 fine, no points
No Mirrors - Non Endorsable - £30 fine, no points
Number Plate - Non endorsable - £30 fine, no points
However be aware of using a vehicle in a DANGEROUS CONDITION.. £60 fine and 3 points if offered a fixed penalty, or more if summonsed to court.
It's just a rat bike that's all, everything's pukker and correct except the indicators and mirrors (which aren't fitted).
If the bike was one year older it wouldn't be an issue as I believe they only became compulsory in 1984.
I've had loads of old bikes without mirrors and indicators, I actually believe it's safer in some respects because it forces you to look around, rather than relying on mirrors and car drivers really do notice hand signals.