Only Metric/Imperial holders I know of would be the YCC Collets. Here in the USA mine was set up with the YCC Metric Collets, But used straight collet adapters for the End mills and drills.
I suppose the tool bushing would be English instead of Metric, but nothing a sleeve couldn't fix.
As far as parts I would keep. Controller rack assembly, drives, servos, encoders, control panel, display, lube pump, spindle unit, tool chain, c_hooks, all VDI tooling, chip shields, parts catcher. Maybe ball screws. All these parts could be boxed and placed in overhead storage, with the exception of the spindle unit. Some of these parts are getting a little hard to come by these days, Mazak can still provide most of them, but at a long lead time and a high cost. Us home shops usually can't or don't want to afford Mazak pricing...lol
Regards,
Heli