Nice.
You should have no problem with your custom dies made to match the fire-formed cases.
Conrad's neck was about 0.300" long on his .35 B-W, and IIRC mine was too.
Fire forming brass can be as simple as using a .357-handgun bullet upside-down,
loaded long enough to headspace with base of the pistol bullet into the rifling.
Use a 158-grain handgun bullet and a usual starting load for the 200-grain .358-caliber rifle bullet.
Nice plinking while forming brass.
New .35 Whelen brass is the easy choice for that.
