Dave,
I inserted some pictures in the post above, I hope they are sufficient to show you what you wanted to see. I spent half the day today turning down barrels from these and here is what I came up with for sleevers. I won't promise that yours will be the same length because it depends somewhat or what size the holes in your monoblock are. I turned mine down to a .940" diameter stub that is 2.2 inches long. The monoblock was just over an inch in diameter at the front. I turned the stub partially and then cut off the part that were notched into the barrels from both sides to allow extraction. Then I finished the stub with the shoulder complete. When I got finished up I had barrels that are 23 3/4 inches long and weighed 1 pound 3 ounces each. The smooth bore barrels I took off weighed 14.8 pounces each. That means that the new rifled barrels will weigh 1/2 pound more per pair than the smooth bores did. Bob