Trigger parts are interchangable, but if you're gonna go to the trouble to swap em out, you might just as well do a trigger job on the bad one, it's not that hard, download and read the trigger hone links in the Centerfire FAQs for more info.
A trigger job at H&R will take the same amount of time as fitting of an accessory barrel, 6-10 weeks, unless they're doing warranty work at the same time, they can expedite that. If the trigger is already under 5lbs, they've been known to charge $20 for the work, they aren't always free.
Tim