My 68 WQ 400 with MT has vacuum ports in the front and back of the cannister on the distributor. When you buy the vacuum hose kit from Year One, it includes a diagram. Mine is long gone, but perhaps someone else has one...

I had always thought that every 400 had chrome air cleaners- thats what the Michael Lamm book said. I think a lot of people trashed their tops when they became faded and pitted, or when they put that "must have" Moroso air cleaner on...