Shotgun Boogie Gun Works adjustable trigger kit for competition rifles, model Uberti ’73
Includes trigger, two trigger springs one is ~1 lb and ~1.5 lb, washer for the trigger spring, screws, pin and safety bar spring.
While this kit is easily installed, it is not drop-in, it requires fitting by a competent Gunsmith.
See also the article in Cowboy Chronicle January 2015 from Larsen E. Pettifogger. Pages 36-45: