I am not sure I understood your question, but I will submit 2 answers. If you are planning on sending it out to someone for the choke work it would be best to e mail them as to their requirements as to barrel thickness etc. They will be happy to inform you as to outside and inside diameters needed for their tooling.
If you are planning on doing this work yourself I think you will find the cost very high, unless you are going to offer the services to others to defray the tooling cost. If not you can Google up several gunsmiths that do the work. I have used Mike Orlen, great work, quick turnaround. I hope this helps.