It's hard to see much from photos and as you say it would need to be closely examined by someone in the know.

One thing I did notice is that the extractor body is out of alignment with the barrel face.
This is visible on the left side where the extractor is sitting proud, but is flush on the right barrel side.
There is also a witness to this on the left side of the action face.
Most likely caused by a bent extractor rod.

This rifle does not really appear to have been thrown together in some back yard shed.
The quality of the fitted parts as shown in the photos appears quite good.
IMO whoever did the conversion was capable of producing a good result.
Still needs to be checked out before doing any serious dealing though.
That goes for ANY double, regardless of make, model, age, or supposed condition.