why a custom built converter isn't for everyone....

Exactly what I mentioned earlier. People call and tell their build, and most of the time one of their "off the shelf" already built converters is close enough to fill the bill and that's what they ship. People get all shook up because they want to think every turbine was fully implemented with their build, and only their build in mind. So many builds are so similar that the need to weld every tooth on the ring gears especially for Jon Doe's car is ridiculous.
In other words, every 408 stroker pushing 380-450 hp in a Duster with 3.55 - 4.30 gears would be very happy with part number XXXXX. And that's what they pull off the shelf. Less % than what people think actually get a specific TC that was never built before for their application. If it was built 10x before, then isn't that the same as "off the shelf"... ?? LOL