Brent, I have a .22LR #1 Rolling Block done similarly. Not as pretty as your Winchester. I bought it from a friend with a 20" half octagon .22 barrel on it and converted to RF. The round part of the barrel was stubby, and looked odd, but shot great!
I took the gun to John Taylor and asked if he could lengthen the barrel without harming the existing barrel. We decided to cut down the round part of the barrel and add a 20" sleeve over the round part and butt it to the octagon transition of the barrel. So the last 10" internally is now .45 caliber as viewed from the muzzle. After installing the "bloop tube" I took it to the range and test fired it. The groups were as tight as before, or maybe even a bit better!
I reblued the barrel afterwards and reinstalled it on the gun. The repair is invisible and the gun balances extremely well, plus looks appropriate too. My pictures are poor, and my big foot doesn't help either!
