Another book og interest
"Modern Rifle Shooting From the American Standpoint"

Modern rifle shooting from the ... - Google Books
The section on the Kragicon is short but informative.

There are alterations to the trigger for target shooting that I doubt anyone here would want to do, but examining these instructions would allow you to recognize whether such alterations had been done to a rifle you are interested in.

If such alterations have been done to a rifle they'd be of historical significance rather than greatly detracting from collector value as a modern alteration would.