Other than the suntan I don’t think there’s much difference between a classic rough and tough good guy western movie gunslinger and a knight errant. Irons could probably pull it off, Tiberias in Kingdom of Heaven did have some world weary but still noble that I think is important for the Roland character.
Yes and no. The Gilead of Roland's youth was a place of high culture and strict social rules which forged a lot of Roland's character. The gunfighter archetype doesn't necessarily have that courtly foundation. Certainly there's a lot of overlap between the two, but the classic gunslinger needs no past (i.e. Eastwood's High Plains Drifter). A knight's training, upbringing and pedigree are essential elements of his legend.