"Armour Alloy II" was Thompson/Centers proprietary hardchrome finish. They offered it back in the late 70s thru mid 80s before they started making stainless Contenders. All they did was coat existing blue frames and barrels. Since the finish has a certain thickness (maybe a few thousandths) it's impossible to fit the Base Pin from a standard Contender. All the conversion consist of is reaming out the hole in the barrel lug.
When T/C came out with real stainless Contenders it made AA obsolete. They got stuck with a bunch of AA barrels in inventory and they're still selling them on their internet site at bargain basement prices (I'd say "fire sale prices", but that's a sensitive subject with T/C). My NIB 14" .44 Mag barrel cost $123.85 delivered.
Unless someone has a better idea I'll probably use some extra fine silica/carbide sandpaper wrapped around a wooden dowel to open up the hole. Someone posted a few months back that that was all he did and it worked fine. AAII is harder than Chinese arithmetic, way harder than stainless steel and more corrosion resistant as well. -- Kernel