Naim Nac 52 & Nap 135's are Classic pre/power of very high standard
IMO it takes something to really come close this combo
As for the SC, the new DR may be a better choice, no idea what they charge for conversation or service, sure Naim themself have a long waiting list so try alternatives, also to get a better Price, Naim have recently done a jump in prices
Fully agree on Class A in Sheffield with which I have excellent experience, fully recommended and he keeps things original which should be advised for best possible resale value.
I thought Witch Hat would offer a standard service but in doubt, sure he has the knowledge beeing a former Naim employee
The issue you should rethink:
You are buying at least 10-15 years old stuff, in fact everything is in need for service unless allready done offcourse, this is vital and you should investigate precise expenses/shipping? to add Price
Once done forget the gear and enjoy, one hell of a combo, hope you succede with answer to all your threads, speakers etc..IMO these do not need to be purchased based on the price only, on the contrary, I prefer my Eur 300 ES14 to a pair of very expensive ProAc.