How reasonable are copies of Schwing's book "Winchester Slide Action Rifles - volume 1" on your side of the pond? That is generally considered THE authority over here.
You might get help at the Two Ponys website or you can always post your question over in the Winchester section of Rimfirecentral.com.
Two Ponys They could be "cleanup" guns late in production or a replacement barrel due to corrosion from the ammo of the day.