the design is some what typical of 16th Century Common Handguns, Scots and Cromwells "Roundhead" cavalry would have carried a pistol resembling the one Pictured.
Online sources may be of some help, but I often opt for the restoration if it will not actully reduce the value of the item-go ahed, but be mindful that you may chamging a $1000 pistol into a 500 pistol, which is fine.
This is assumning the guns is not collector grade and is fireareable or attractive enough to clean up.
Frankly, I would leave it alone, except for some minor cleanup
Bruces's comments seem on the money and I have posted an Italian pistol pic from the period.
Outwardly the piece resembles some 16th Scottish designs and I will post one.
But I could not find and clear replication of the weapon in my library.
I am inserting several pics that come close to the design of the arm, which would seem to indicate, with the comments of your gunsmith, that the weapon is a 'trade" gun of o copy theory.
The real Italian pistols of this design would be quite valuable.
Obviously Flatyderman's Gun Value Guide does not cover this period.
However, the shape is remininscent of those used shown in cavalry training pictures dating from the time of the "New Model Army----but I do thoink it is on of those, even a set of armor from that period found in Roanoke was quite deteriorated.
I will just post some pics for an old history of the gun.
But, based on the pic an the opinion received, i would do anything yet.
Other comments: The weapon is detiorateed and has been bound together twice with wire.
There is some evidence of good constructction and ornamentation.
I am going to sau just clean it up by hand a little and see what happens.