585 nyati barrel questions

[Hugh1234]

Hello I am plaining on building a 585 nyati rifle from a 1917 endfield. I need to order a barrel and I have a few questions. What is the best barrel length for it? , is it a good idea to add threads for a muzzle break ? , what is the best twist rate for it ? And what is the best barrel contour size for it ? any help would be appreciated.