The question is sort of irrelevant to the EFI used. I am running a Microsquirt system with dual 1bbl TB's on a reproduction dual 1bbl intake for my flathead six. I had to make a 1" adapter to mount the throttle bodies to the intake and I tapped both adapters to feed a common source to the MAP sensor. With the 4bbl TBI setup you still need a common vacuum source but it doesn't have to be anything huge, just enough to tie both sides together. A thick gasket may do the trick. Pic shows my setup to feed the MAP, if you had stack EFI you'd still need to tie all eight setups together to provide a common source.