gcoding I'm pretty sure the spindle would have to go back to Colombo to be made into a atc spindle. An atc has a hollow shaft in the middle that contains the pneumatic gripper that holds the tool holder. The holders are much larger than what you currently use. My thought would be to sell the manual and use the money toward an atc. BTW they are not cheap.
http://www.pdscolombo.com/index.htm
These guys would be the ones to talk to. I missed a brand new 9hp atc colombo on ebay that went for $2500.............new they go for around $7000.
Mike