I generally concur with Mike's assessment of southern rifle barrels. I believe most were made for small game hunting and/or target shooting and were usually shot from a rest or prone. Unless, you are building a chunk gun, you probably don't want a really authentic barrel size and profile. However, all the original rifles I have seen had swamped barrels, although very slightly swamped. What Rices Southern Class does is give you that very slightly swamped profile with a slimmer breech.
I have used the Southern Classic in 45 and 50 for customers that are using them for hunting and target shooting. Both had problems with recoil that required considerable fine tuning of the fit and/or load. Personally, I think the Southern classic is too light in 45 and 50. I think it is more appropriate in 40 caliber or less. In the future, I am going to recommend a B or C weight barrel for clients who what 45 or 50 caliber, but I guess a lot depends on how much you plan on carrying the rifle.