All I could find was this..
Back issues of "Arms Collecting, formerly known as The Canadian Journal of Arms Collecting"
Vol. 23, No. 2 (May, 1985)
Howard, Gordon T., p. 60-62 The Key Gun.
http://www.manatarmsbooks.com/mrsinventory.html
The page also contains the word Londini , although not in conjunction. Might be worth writing them an email at least though. It also contains the world dolep in this entry.
Vol. 40, No. 4 (Nov. 2002)
Forman, James D. Andrew Dolep, Gunsmith to His late Highness Prince George of Denmark. pp. 119-121
Here is a bonhams lot entry, from early this month for a flintlock pistol from "Andrew Dolep Of London, Circa 1690" It mentions "London proof marks and maker's mark"
http://www.bonhams.com/cgi-bin/publ...eItemNo=3496047&iSaleNo=14885&sServer=&sPath=
It appears that it sold for about $7,601.13 USD
If what you have there is real.. it could be worth some serious money. I might suggest contacting bonhams at a usa location. Heres a list of them.
http://www.bonhams.com/cgi-bin/public.sh/pubweb/publicSite.r?sContinent=EUR&screen=USAreps