I just received a "Spring Spectacular" flyer from DGW. On page 21 they have 3", 5 1/2"' 5", barrels for 1851, 1860 and 1858 revolvers. I ordered a 5" "Sheriff" barrel for my 1851.
I think the only thing you have to do is put the new barrel assembly on. It comes with loading lever, the whole works.
'Loose