I would say from your photo that the breech pin is almost certainly original. The shape and knurling are identical to other Dolla variant 3 examples, and distinct from the variant 4 . The only slight issue is that yours has a single start thread instead of the more usually seen double start thread. However if the thread is a perfect match for your gun then all this means is that yours is probably a late example. The single start thread was used in subsequent variant 4 Dollas. A subtle but interesting variation but unfortunately doesn’t add to the value (which I would put at £50-70).