Cleanliness is key to achieving good runout control when assembling tool holders. Small particles or oil in a tool holder can cause large runout of the cutting tool, deceasing tool life and performance.
Hydraulic chucks are an excellent choice for high accuracy applications due to their ability to maintain runout accuracy over an extended period of time.
The concept of using guide pins to load large fixtures has been around for a long time, and it even applies when incorporating Unilock zero-point clamping systems in your fixturing.