Bernhard,
As much as you seem to be interested in these bikes you should acquire some factory parts manuals to answer simple questions like this.
The parts books have different part numbers for 1961 88ss exhaust pipes than they do for 1962 88ss exhaust pipes, maybe because those two models also used different cylinder heads. The 1961 88ss did not have the 650ss style head, but the 1962 88ss did.
Interestingly the parts book lists three different sets of pipes for 1961-62 standard and Deluxe 88, 99, 650 bikes. Probably because although the 88 and 99 have the same head, the 99 has a taller cylinder, and though the 650 for all practical purposes has the same cylinder deck height, it has a different cylinder head than the 88 and 99 standard and deluxe.
At this point 60 years later unless someone with a set of pipes has actually tried fitting them onto a particular Norton Dominator model, I would have a lot of doubt that they would know exactly what they would fit and what they would not. Also the information in factory parts books would apply to original Norton pipes, but if a set of pipes are manufactured by some aftermarket company all bets are off.
I have a brand new set of original Dominator pipes hanging in the garage that would not go onto a 650 because they were too short vertically to drop below the timing-side of the engine cases. When I get the chance I will try them on a model 88ss with it's shorter 8-fin cylinder and see if that makes enough difference to let them fit, if that does not work then perhaps they are for one of the older style heads.
