Might as well put a wrench in the works here. Anything you can buy off the shelf and put together to me isn't custom. Anyone with a lathe and some basic instructions can thread and chamber a barrel. Calling defiance for an action, McMillan for a stock, timney for a trigger, Krieger for a barrel and having it assembled is something that almost anyone can do.
Custom to me is wood and steel and something you can't buy off a shelf. A craftsman takes a block of wood and carves out a stock to fit you, metal work is done in the exact style you specify, if it's a big boomer an extra recoil lug is machined out of the barrel and the checkering is done in the style that you desire. Not pick out of these 4 templates.
Ordering a "custom" rifle from Dakota or Cooper isn't any different then ordering a new pickup or car and specifying what options you want on it.
Custom to me is a rifle built by one man from start to finish that cannot be duplicated other then by him. I'm not saying build action, trigger and barrel; I'm saying that he can take a rough action smooth it out, hone a trigger to where it's reliable, safe and crisp, turn a barrel to a custom contour etc. Factory parts from different manufactures assembled to build a rifle is just ordering a factory rifle that is tailored to your taste. Custom is a one off job. Built is a assembly of parts that you specify but can be duplicated in a instant by almost anyone.