The vacuum chuck assembly I bought from William Nobel at  www.wbnoble.com .   He also sells cheap faceplates using a large washer welded to appropriate nut to match your lathe.  Not pretty but they work fine.  Also you will find all the information you need on vacuum chucking systems.  Putzed around for several years with my own home built and cheap commercial types/components for vacuum chucks.  If I would have gone with his product to start with I would have saved money and hundreds of dollars in profanity.  The pump is pulling 24" which based on the 6" faceplate gives 225 pounds pressure holding the platter in place.   I also use the Oneway spindle vacuum adapter which is typical Oneway quality.  I consider Oneway the Gold Standard.  When I bought the 3520A, cost was not serious consideration, I just didn't see that the Oneway was worth the extra $1500 plus it didn't have the sliding head stock.  The platter is made from sinker cypress and red heart.  Behind the lathe you can see the 30" fan I use for dust control and under it is the door so I can sweep the shavings outside.