damngato,
Subject to correction by other forum members that actually know something,I think the following.The gun likely never went to London, it was built on a action type that Anson & Deely from London held the patent on. It was made and proofed in Belgium. A.Francotte was a well respected maker, which I believe is still in business. Von Lengerke & Detmold were the US agents for several Foreign makers, including Mauser and others. I believe you should have the gun repaired, to replace the missing pins,including the hingepin, which should be carefully fitted. Once it is repaired, you can decide whether you want to spend the money to have it restored.It will still be your fathers gun, even if not restored.
Mike