Swenson used two marks that I know of that were spelled out A.D. SWENSON (first line) Gardena Calif OR Fallbrook Calif or just CALIF. (second line). I have also seen just A. D. SWENSON and no second line. Lots of "circle S" stamps. Swenson marked anywhere and everywhere, often to cover mistakes or dings done in the shop according to those who knew him or hung around his shop. The only person I can verify that actually worked for Swenson is Wayne Novak and I suspect he has a wealth of knowledge , much more than anyone else on Swenson guns...Ken Hackthorn would be a close second I bet, as would Walt Rauch.
The trigger guard is easy to do with heat and a swaging bar. Nothing is removed if done right.
There have been a half dozen articles about Swenson in recent years. I know of one more coming soon. I suspect there is as much info here on this forum as has been written. I know the pictures are better and of more guns that anywhere else I have seen published. More to come here BTW.
The BCP CD does have a good section on Swenson...as well as Heinie, Garthwaite, Vickers, Novak and some photos of work by Hoag, Colt, Bilby, Wilson, Yanek, Krebs and Jardine. They cost $20 delivered, even to Canada :grin: