Actually, #721-N63/B is the flanged
750 pipe set that would normally use the long '750' lockrings so you may have to either double-up on the crush washers or fit your 'short' 850 lockrings with the collets (if they will fit?) and crush washer, because, due to the 850 models having the balance pipe each lockring could only be fitted over the head end of the pipe so the end flange could not be used, therefore, collets, a shorter lockring and grooved end fitting (pic below) were used on the pre-flared 850 pipes so there should really be three sets of pipes for 750, pre-flared 850 and flared 850.
750
Norton Exhaust Pipe Commando Roadster 750cc 1970-73 OEM: 06-3375, 06-3376 British made classic motorcycle exhaust system
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850 (Mk2A is not entirely correct)
These will fit the Norton Models: Commando MK2A 850cc OEM: 06-3397, 06-3398 This is a complete set of two exhaust pipes required to fit a MKIIA Norton Commando. 2 pipes without balance - 2 single pipes only. Exhaust Pipe Dimensions: Inlet Size: 1+5/8 inch
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Mk3 (also late Mk2A)
Norton Commando 850cc MK3 Exhaust Pipes Set - WITHOUT Balance. Complete set of pipes to fit a MKIII Norton Commando. 2 pipes without balance. Outlet Size: 1+3/8 inch (35mm). OEM: 06-5256, 06-5257. Chrome plated - made in England
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