I can see the double triggers on the Viking, but am having some problems seeing how the first trigger activated the second.  I guess the first trigger just operated the hammer and the rear trigger released the sear...

I take it none of those guns are any longer in your possession?

Re: galling on early stainless guns.  In a 1980s review of the AMT Hardballer Jan Libourel, who gets my votes for one of the finest, most honest gun writers to ever put pen to paper, reported that he was advised at the time by AMT to use white lithium grease on the rails of the Hardballer, and after using it liberally he had no malfunction issues at all.  Today we can buy a pistol specific white lithium variant in the form of Lubriplate Aero, which is what garage door mechanics use to lube door rails.  It's the perfect viscosity for pistols. I have also used pure white lithium grease, sold by the tub, and while it works, I believe it to be too high viscosity for pistols, it's quite thick, and tends to dry out too soon. 

I realize today's stainless pistols use different grades for the stainless between the frame and slide to avoid the galling problem altogether, so this problem might be considered moot by some, but stainless is steel is even today not as buttery smooth in operation as well-polished carbon steel, in my opinion.  The recommendation for white lithium still stands today as a good one for stainless pistols, and still works very well for all pistol rails.  Company info on Aero below.

Image below from Mark Freburg - Image Title: Lubriplate Aero
Image Info: Lubriplate AeroLithium Based, Low Temperature Grease •Outstanding compatibility with seal materials•For applications to -60 ° FFor cold temperature applications down to -60°F. / -51°C. Provides low-torque start-up capability, excellent corrosion and oxidation resistance and wide compatibility with metals, plastic, and rubber. Excellent for firearms.