What kind of rifle are you going to use these cartridges in? If it is a single shot, the case length is a non-issue, as most long range BP shooters use just enough neck tension to keep the bullet from falling out and no more. In single shots, crimping is not required nor recommended.
If, on the other hand, you're going to run these through a lever gun, the length becomes important because of the need for consistent crimping.
So, first, what rifle will you use these in?