How many commando owners know that from the 1949 model 7 that the exhaust ports and therefore the pipes were each angled (splayed ) 20 degrees from straight ahead. Starting in 61 with the manxman the semidown draft head splay was 40 degrees making the pipe bend more difficult to lay close and be tucked in to the frame rails. A Norton factory compromise was to have the pipes have a offset outlet at the head/ exhaust spud, I have seen it on 71, I think it was on 72. Original 73 750?
By the 850 the pipe skew was gone. Pipe part numbers have changed probably reflecting the factory changes. I doubt the aftermarket's recreations of early pipes are correct and are some of the cause of the kicker hitting the mufflers.
FWIW current aftermarket "SS" pipes have the skew in them.
The above is of course all speculation and if wrong, better factory documentation by experts will come forth. I hope