You know, this would be a great time to install a oneshot lube system. Since it will be CNC a motorized one would be even better. It will extend the life of the mill. And since everything is in pieces...
There is one more option for using the Z that you have not mentioned. It is the method that was used on my Supermax. It consists of a 4" ID air cylinder. the rod is removed replaced with the screw attached to the piston. the nut rotates on top of the cylinder on a thrust bearing. A timing pulley is fitted around the nut and is belt driven. Then the screw goes up into the knee. A pressure regulator is then used to adjust the pressure through the bottom port and balances the knee. Mine balances out at around 40 PSI (Guess that meand my knee/table weighs about 500 lbs. When the knee goes up the regualtor keeps it at 40 and when it goes down it dumps to keep it at 40. I think this is the regulator used on mine: http://store.norgren.com/US/en-US/ca...-300-RGLA.html
Seems to work well. I have done some peck routines and it seems pretty responsive. Plus it leaves your head so you can do manual drilling and the like.