View the below linked document that shows how to add the External Isolation Valve (PK-VALVE-20M) to the drivers connector of the Contamination Prevention System (CPS-20M)
There is an updated drawing for stacked mode in the 6270A Operator's Manual that was updated in April 2018. It's available on this page, https://us.flukecal.com/category/literature-type/product-manuals
Refer to the following sections in the 6270A Operator’s Manual
Contamination Prevention System (CPS)
External Driver Communication
External Isolation Valve
System Stacking
Contact Fluke Calibration Pressure Calibration Technical Support at the below link or by calling +1.877.355.3225