
You are being sensible with this enquiry. They should both fall within the Breed Standard, and not just with size btw. If your gut instinct tells you this may not be a good idea, then refuse. Over the years I had males at public stud, I turned away more than I accepted - mainly because I knew the bloodlines and whether or not they would nick. Be aware that when things go wrong, and they often do despite all the paperwork saying ok, it's ALWAYS the 'fault of the stud', whether true or not!! And others within the breed will be listening.
Re the risk of a C.Section - this could always happen regardless of size if a puppy presents in an awkward position.
But what about construction - do they both carry the same faults? Temperament? And so on. Again if part of you says this isn't a good idea, say no. Have the two lines been combined before (in other matings)? With outcross matings, you may get the best of the best, or the opposite. Remembering that the owner of the stud dog is 50% responsible for how the offspring turn out.