If the Trapper was made mid '80s or later, more than likely they'll work fine, earlier some parts may or may not, anything made '87 and later will fit, '86 and earlier H&Rs were made by a different company than the currrent H&R1871, there's a build year list by serial number prefix in the FAQs sticky. Are you sure it's a Trapper and not a Topper?
Tim