Probably just a stripped lower and a LPK. You'll also most likely need a bushing to fit the large hole upper on the new small hole lower. You can get it assembled or separate. You dont want to/ can't use the full auto parts in the semi gun. Keep in mind the new lower will not match in coler to the old colt parts. Also some of the real early colt stuff did not have all the chrome lining that current issue stuff does.