??? - original mufflers - ???

Sileencers were subject to rust item and were vulnerable to damage in an otherwise insignificant accident, so they may have been a replacement part on an otherwise original motorcycle. But I'm with others -- these are in some ways slightly different to stock silencers and in other ways correct in details. I can't help further, I'm afraid.

L.A.B. said:

...

Although supposedly Mk3, that type of flared exhaust pipe was introduced on the Mk2A.

The flared pipes (065256 & 065257 same as 850 Mk3) are listed in the Mk2/2A supplement for Mk2A ...

https://andover-norton.co.uk/en/shop-details/20631/exhaust-pipes-pair-850mk3-balanced

Click to expand...

Interesting, If that's the case and he has the flared header with the balanced pipes, that would indicate his may have originally been a 2A, which would have had Black Caps, not Pea Shooters.
Hence his Pea Shooters are not original, or at least didn't come with the bike.
But then again, nothing is for certain with Norton.

MichaelB said:

Interesting, If that's the case and he has the flared header with the balanced pipes, that would indicate his may have originally been a 2A, which would have had Black Caps, not Pea Shooters.
Hence his Pea Shooters are not original, or at least didn't come with the bike.
But then again, nothing is for certain with Norton.

Click to expand...

I don't think my 74 was originally a Mk2a - while it has several Mk2a features, one major item it doesn't - the "canned-ham" air cleaner assembly. but like you said, "nothing is for certain," and, unless you have a time machine. who knows what the original owner or previous owners did in those early years.

then again, somewhere along the line, someone could have replaced the original header pipes and kept the original mufflers. If you believe in the infinite multi-verse theory, anything's possible.