360-1 Casting better?

From a manufacturing point of view it makes no production, logistical or financial sense to be casting (or fabricating in any way) something considered better with the rest of the "run of the mill" parts on the same line with the same part number, tooling and production individuals. If they were better in some way why did they end up in production vehicles? While there will be variations from tool to tool, shift to shift, operator to operator, from an mass assembly point of view they would all move on to be built for their intended production use.