You are correct I forgot those existedAn interesting original vacuum source on my 1960 corvette's 283 V8 is the use of a hollow carb mounting stud installed in the manifold for the right rear carb mount nut. This may be useful to you. Available at C1 Corvette supply houses like Corvette Central.
Here's a picture of one.Never seen a Chevy V8 with a 2 stage fuel pump hooked to wipers but I have seen the rear of the carb used as the source on orginal 55-57.
Are you sure thats for a Chevy, I remember the day when the average salvage yard had dozen of 55-57s and I never seen one of these on a car.Here's a picture of one.