The real Whitworth was a pretty fascinating rifle. It had a hexagon bore of .451" caliber, firing a fitted bullet which was quite long and heavy for the caliber. It actually was quite effective at long range. We can still buy very accurate representations manufactured by Pedersoli in Italy.
Most did not have a scope mounted. They used an elevating rear sight like this:
Those that did wear scopes were pretty similar to this:
Some guys actually used to shoot these in our long range matches. More conventionally rifled muzzle loaders did better, such as the Gibbs, Rigby, and Parker-Hale. Against breach loaders, though, none did well, as they had to "break position" to stand up and load between shots.
For a very interesting read on the development of long range riflery in that era, just post Civil War, google "Sandyhook Tests". Yes, these rifles could kill a man at 2,000 yards. If he was having a really, really bad day...