We have a nice 7" polished stainless dual diaphram booster with master combo. Comes with the proportining valve and lines from the master to prop valve.
These things are powerfull, use little vacum and package nicely.
And they are only $250 for the combo
I need a better pic. But here is one we used in a 57 Chevy we just finished with a 572CI tall deck motor.