It looks to me that your Father may have found a barrel.
The butt looks as though it is homemade and the it does not look as though a lock has ever been inlett into the butt. With the number of fittings that would be needed to bring the pistol back to something like decent it would be very costly.
Is this possibly a wall piece? There does not appear to be a flash hole for the pan? (And no pan).

It is possible to buy a percussion or flintlock pistol for a little as £50 - £130 so I don't think it is worthwhile trying to restore it. And, judging by the amount of corrosion on the outside of the barrel, it may be unsafe to use.

If it is a genuine barel it is a nice keepsake, but I would do as you suggest, keep it as a paperweight.

This is just my opinion.

Atb