Here is something to consider on the barrel. First turn a length of blank down to .540 and thread the end with 36 to the inch threads, so it will go into the frame and slightly past where the cylinder will be. Then take a K frame 38 barrel the length you want (available on Ebay if you don't have one from original donor frame). Drill it and ream it to .500. Then mark the new barrel piece where it goes into the frame. Then turn it down to .5005-.501 on the forward portion with a square shoulder where it goes from .5005 to .540. Then the barrel goes into a solution of kerosene and dry ice. This will shrink it. The frame goes into the oven at say 350f. It expands. Using heavy gloves quickly shove the 2 together. Have a extra length of barrel "liner" that is slightly tapered to guide the start. Should get a shrink fit that will stay forever. The shank that goes into the frame will be full sized and it will all be plenty strong and thick enough for a .312 bore. Way better than just putting a thin liner in a barrel IMHO. Basically just the exposed portion of the old barrel into a shroud to cover the new blank. I thought long and hard about making a K32 before I broke down and bought a 16-4

Reason I suggest this is because fitting the front lug is a real pain. I did the one on my 45 cal revolving carbine by machining one from an old barrel so that it went into a dovetail machined into the new barrel. Took some measuring and figuring to get it exactly the right height and location and blend into the barrel right.

I have never done this with a barrel, but it should work well. Have done it with some other things and it worked well. Common for fitting things on shafts.

If you need a tap to clean up the threads in frame or a die to clean up the threads cut on the shank let me know. I also have the tool to face of the shank for BC clearance and to cut the new forcing cone. I bought a tap for N and K frames and used them to make a chase die from A2 and hardened them.