Be careful when communicating with someone that says they have a Nomad Mk I. Some people assume that the older Nomads that were brazed in the UK and fitted with derailleurs are Mk I, which is inaccurate.
Mk I Nomad is very similar to Mk II, but Mk II has some extra reinforcing where the downtube meets the headtube. You can see that extra metal welded onto the downtube and headtube in the photo.
I am not sure if all of the Mk I Nomads had S&S couplers or not, they might have. That was an option for Mk II.