Here is the Chinese solution, machine only, cast iron , without motors , smaller envelope, seems its quite worth to DIY it, price wise .



This below also should be taken in consideration when designing the head. In fact you will need the motor, the spindle and the air cylinder in your hands, before you continue further with your build after a certain point.

2Ton( 2000kg) air cylinder 13mm cnc piston cylinder for BT30 ATC Spindle of CNC milling booster cyliner FL003D