https://andover-norton.co.uk/en/shop-drawing/147/exhausts-mufflers-passenger-footpegs
That's the Mk3 (and later Mk2A?) type flared exhaust pipe so there should have been collet 06.5260 (or broken into two parts?) between the exhaust lockring and the pipe flare?
Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
And, I think I see an incorrect (06.3995) sealing washer...
Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
...behind what looks to be the correct (06.5259) spherical seating...,
Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
...as 06.3995 washers wouldn't normally be fitted with that type of flared exhaust, only collets and spherical seatings.
Also, the long reverse cone Interstate silencers you have shouldn't fit that type of flared exhaust pipe system!