As of yet I have no pics of the top cover hold-open, but it's basically just a cammed fitting that uses spring tension. Here are some diagrams: http://www.impactguns.com/library/1919/1919.htm
Actually mine IS a SA, but here's the good part. It has a VERY light trigger pull, and I have timed mine with a stopwatch at 120 rounds in 15.2 seconds, which is right at 8 rds per second! Not quite the rate of a FA, but with the "cannon-like" sound a 1919 makes, it sure gets the neighbor's attention!
The secret to SA in mine is in the sear. When the trigger is pulled, the sear drops and releases the firing pin just like a FA, but the design of the SA sear makes it "catch" the trigger each time the bolt moves forward. The FA sear doesn't "catch" the trigger until the trigger is released.
All the rest of the parts are (or look like) regular GI parts.