Over the years there have been a number of domestic smiths/companies who performed mono-blocking on vintage guns. The Lefever gun company in New York state (this was a grandson of Dan Lefever-Bob, I think?; not the maker of original LeFever gun) provided this service for years and likely did hundreds of sets of barrels (I believe the gentleman who actually did the barrel work purchased the company when LeFever retired, Andy Wojowitz?). At any rate, LeFever did several barrel sets for me; as has Buck Hamlin of Pevely, MO and Del Grego. None of the sets done for me have any proof marks or stamps by any workmen; but all were proved in some fashion and always gave great service. DeL Grego also provided mono-bloc barrels for his Parker customers, but this work was a subed out to Lefever. Several transplanted English gunsmiths here in the US do/have done mono-blocking, as well as some companies specializing in barrel work. This practice was not uncommon at one time; however, given the renewed interest in Damascus barrels and the on-gowing research into their strength (apparently much stronger than we were lead to believe) and the very high cost now of mono-blocking, I know of no one who has had such work done recently. My own opinion these days is that these old barrels (Damascus or steel), assuming their integrity remains sound, should be preseved. If someone wishes to use his gun, all kinds of date is available now for low-pressure loads (which we did not have 20 years ago) so that the gun can be safely used.