The nominal neck length for the 416 Taylor and 411 KDF is .345 and for the 416-338 its .425 but the actual length would vary depending on how much the parent case grew or shrank during fire-forming and how long the parent case was to begin with. Of course, the same comments would apply to any wildcat.
The 411 KDF was originally a wildcat but I understand that QUAL CART now makes it. My wildcat version also has a longer neck (.385") than the Taylor but it does use a smaller diameter bullet. That’s why its important to determine exactly what the diameter is on your cartridge. If yours measures .4115 at the case mouth it could well be a KDF. The original KDF was loaded with custom made bullets having a cylindrical section past the case mouth. Mine meaures .411 and I THINK that same diameter continues on all the way to the base.
But in the end, don’t forget that you have a wildcat on your hands. And I’ve learned a long time ago to expect just about anything when dealing with them.